summaryrefslogtreecommitdiffstats
path: root/arch/x86/mm/tlb.c
diff options
context:
space:
mode:
authorDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 18:49:45 +0000
committerDaniel Baumann <daniel.baumann@progress-linux.org>2024-04-07 18:49:45 +0000
commit2c3c1048746a4622d8c89a29670120dc8fab93c4 (patch)
tree848558de17fb3008cdf4d861b01ac7781903ce39 /arch/x86/mm/tlb.c
parentInitial commit. (diff)
downloadlinux-2c3c1048746a4622d8c89a29670120dc8fab93c4.tar.xz
linux-2c3c1048746a4622d8c89a29670120dc8fab93c4.zip
Adding upstream version 6.1.76.upstream/6.1.76
Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>
Diffstat (limited to 'arch/x86/mm/tlb.c')
-rw-r--r--arch/x86/mm/tlb.c1323
1 files changed, 1323 insertions, 0 deletions
diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c
new file mode 100644
index 000000000..c1e31e9a8
--- /dev/null
+++ b/arch/x86/mm/tlb.c
@@ -0,0 +1,1323 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/init.h>
+
+#include <linux/mm.h>
+#include <linux/spinlock.h>
+#include <linux/smp.h>
+#include <linux/interrupt.h>
+#include <linux/export.h>
+#include <linux/cpu.h>
+#include <linux/debugfs.h>
+#include <linux/sched/smt.h>
+#include <linux/task_work.h>
+
+#include <asm/tlbflush.h>
+#include <asm/mmu_context.h>
+#include <asm/nospec-branch.h>
+#include <asm/cache.h>
+#include <asm/cacheflush.h>
+#include <asm/apic.h>
+#include <asm/perf_event.h>
+
+#include "mm_internal.h"
+
+#ifdef CONFIG_PARAVIRT
+# define STATIC_NOPV
+#else
+# define STATIC_NOPV static
+# define __flush_tlb_local native_flush_tlb_local
+# define __flush_tlb_global native_flush_tlb_global
+# define __flush_tlb_one_user(addr) native_flush_tlb_one_user(addr)
+# define __flush_tlb_multi(msk, info) native_flush_tlb_multi(msk, info)
+#endif
+
+/*
+ * TLB flushing, formerly SMP-only
+ * c/o Linus Torvalds.
+ *
+ * These mean you can really definitely utterly forget about
+ * writing to user space from interrupts. (Its not allowed anyway).
+ *
+ * Optimizations Manfred Spraul <manfred@colorfullife.com>
+ *
+ * More scalable flush, from Andi Kleen
+ *
+ * Implement flush IPI by CALL_FUNCTION_VECTOR, Alex Shi
+ */
+
+/*
+ * Bits to mangle the TIF_SPEC_* state into the mm pointer which is
+ * stored in cpu_tlb_state.last_user_mm_spec.
+ */
+#define LAST_USER_MM_IBPB 0x1UL
+#define LAST_USER_MM_L1D_FLUSH 0x2UL
+#define LAST_USER_MM_SPEC_MASK (LAST_USER_MM_IBPB | LAST_USER_MM_L1D_FLUSH)
+
+/* Bits to set when tlbstate and flush is (re)initialized */
+#define LAST_USER_MM_INIT LAST_USER_MM_IBPB
+
+/*
+ * The x86 feature is called PCID (Process Context IDentifier). It is similar
+ * to what is traditionally called ASID on the RISC processors.
+ *
+ * We don't use the traditional ASID implementation, where each process/mm gets
+ * its own ASID and flush/restart when we run out of ASID space.
+ *
+ * Instead we have a small per-cpu array of ASIDs and cache the last few mm's
+ * that came by on this CPU, allowing cheaper switch_mm between processes on
+ * this CPU.
+ *
+ * We end up with different spaces for different things. To avoid confusion we
+ * use different names for each of them:
+ *
+ * ASID - [0, TLB_NR_DYN_ASIDS-1]
+ * the canonical identifier for an mm
+ *
+ * kPCID - [1, TLB_NR_DYN_ASIDS]
+ * the value we write into the PCID part of CR3; corresponds to the
+ * ASID+1, because PCID 0 is special.
+ *
+ * uPCID - [2048 + 1, 2048 + TLB_NR_DYN_ASIDS]
+ * for KPTI each mm has two address spaces and thus needs two
+ * PCID values, but we can still do with a single ASID denomination
+ * for each mm. Corresponds to kPCID + 2048.
+ *
+ */
+
+/* There are 12 bits of space for ASIDS in CR3 */
+#define CR3_HW_ASID_BITS 12
+
+/*
+ * When enabled, PAGE_TABLE_ISOLATION consumes a single bit for
+ * user/kernel switches
+ */
+#ifdef CONFIG_PAGE_TABLE_ISOLATION
+# define PTI_CONSUMED_PCID_BITS 1
+#else
+# define PTI_CONSUMED_PCID_BITS 0
+#endif
+
+#define CR3_AVAIL_PCID_BITS (X86_CR3_PCID_BITS - PTI_CONSUMED_PCID_BITS)
+
+/*
+ * ASIDs are zero-based: 0->MAX_AVAIL_ASID are valid. -1 below to account
+ * for them being zero-based. Another -1 is because PCID 0 is reserved for
+ * use by non-PCID-aware users.
+ */
+#define MAX_ASID_AVAILABLE ((1 << CR3_AVAIL_PCID_BITS) - 2)
+
+/*
+ * Given @asid, compute kPCID
+ */
+static inline u16 kern_pcid(u16 asid)
+{
+ VM_WARN_ON_ONCE(asid > MAX_ASID_AVAILABLE);
+
+#ifdef CONFIG_PAGE_TABLE_ISOLATION
+ /*
+ * Make sure that the dynamic ASID space does not conflict with the
+ * bit we are using to switch between user and kernel ASIDs.
+ */
+ BUILD_BUG_ON(TLB_NR_DYN_ASIDS >= (1 << X86_CR3_PTI_PCID_USER_BIT));
+
+ /*
+ * The ASID being passed in here should have respected the
+ * MAX_ASID_AVAILABLE and thus never have the switch bit set.
+ */
+ VM_WARN_ON_ONCE(asid & (1 << X86_CR3_PTI_PCID_USER_BIT));
+#endif
+ /*
+ * The dynamically-assigned ASIDs that get passed in are small
+ * (<TLB_NR_DYN_ASIDS). They never have the high switch bit set,
+ * so do not bother to clear it.
+ *
+ * If PCID is on, ASID-aware code paths put the ASID+1 into the
+ * PCID bits. This serves two purposes. It prevents a nasty
+ * situation in which PCID-unaware code saves CR3, loads some other
+ * value (with PCID == 0), and then restores CR3, thus corrupting
+ * the TLB for ASID 0 if the saved ASID was nonzero. It also means
+ * that any bugs involving loading a PCID-enabled CR3 with
+ * CR4.PCIDE off will trigger deterministically.
+ */
+ return asid + 1;
+}
+
+/*
+ * Given @asid, compute uPCID
+ */
+static inline u16 user_pcid(u16 asid)
+{
+ u16 ret = kern_pcid(asid);
+#ifdef CONFIG_PAGE_TABLE_ISOLATION
+ ret |= 1 << X86_CR3_PTI_PCID_USER_BIT;
+#endif
+ return ret;
+}
+
+static inline unsigned long build_cr3(pgd_t *pgd, u16 asid)
+{
+ if (static_cpu_has(X86_FEATURE_PCID)) {
+ return __sme_pa(pgd) | kern_pcid(asid);
+ } else {
+ VM_WARN_ON_ONCE(asid != 0);
+ return __sme_pa(pgd);
+ }
+}
+
+static inline unsigned long build_cr3_noflush(pgd_t *pgd, u16 asid)
+{
+ VM_WARN_ON_ONCE(asid > MAX_ASID_AVAILABLE);
+ /*
+ * Use boot_cpu_has() instead of this_cpu_has() as this function
+ * might be called during early boot. This should work even after
+ * boot because all CPU's the have same capabilities:
+ */
+ VM_WARN_ON_ONCE(!boot_cpu_has(X86_FEATURE_PCID));
+ return __sme_pa(pgd) | kern_pcid(asid) | CR3_NOFLUSH;
+}
+
+/*
+ * We get here when we do something requiring a TLB invalidation
+ * but could not go invalidate all of the contexts. We do the
+ * necessary invalidation by clearing out the 'ctx_id' which
+ * forces a TLB flush when the context is loaded.
+ */
+static void clear_asid_other(void)
+{
+ u16 asid;
+
+ /*
+ * This is only expected to be set if we have disabled
+ * kernel _PAGE_GLOBAL pages.
+ */
+ if (!static_cpu_has(X86_FEATURE_PTI)) {
+ WARN_ON_ONCE(1);
+ return;
+ }
+
+ for (asid = 0; asid < TLB_NR_DYN_ASIDS; asid++) {
+ /* Do not need to flush the current asid */
+ if (asid == this_cpu_read(cpu_tlbstate.loaded_mm_asid))
+ continue;
+ /*
+ * Make sure the next time we go to switch to
+ * this asid, we do a flush:
+ */
+ this_cpu_write(cpu_tlbstate.ctxs[asid].ctx_id, 0);
+ }
+ this_cpu_write(cpu_tlbstate.invalidate_other, false);
+}
+
+atomic64_t last_mm_ctx_id = ATOMIC64_INIT(1);
+
+
+static void choose_new_asid(struct mm_struct *next, u64 next_tlb_gen,
+ u16 *new_asid, bool *need_flush)
+{
+ u16 asid;
+
+ if (!static_cpu_has(X86_FEATURE_PCID)) {
+ *new_asid = 0;
+ *need_flush = true;
+ return;
+ }
+
+ if (this_cpu_read(cpu_tlbstate.invalidate_other))
+ clear_asid_other();
+
+ for (asid = 0; asid < TLB_NR_DYN_ASIDS; asid++) {
+ if (this_cpu_read(cpu_tlbstate.ctxs[asid].ctx_id) !=
+ next->context.ctx_id)
+ continue;
+
+ *new_asid = asid;
+ *need_flush = (this_cpu_read(cpu_tlbstate.ctxs[asid].tlb_gen) <
+ next_tlb_gen);
+ return;
+ }
+
+ /*
+ * We don't currently own an ASID slot on this CPU.
+ * Allocate a slot.
+ */
+ *new_asid = this_cpu_add_return(cpu_tlbstate.next_asid, 1) - 1;
+ if (*new_asid >= TLB_NR_DYN_ASIDS) {
+ *new_asid = 0;
+ this_cpu_write(cpu_tlbstate.next_asid, 1);
+ }
+ *need_flush = true;
+}
+
+/*
+ * Given an ASID, flush the corresponding user ASID. We can delay this
+ * until the next time we switch to it.
+ *
+ * See SWITCH_TO_USER_CR3.
+ */
+static inline void invalidate_user_asid(u16 asid)
+{
+ /* There is no user ASID if address space separation is off */
+ if (!IS_ENABLED(CONFIG_PAGE_TABLE_ISOLATION))
+ return;
+
+ /*
+ * We only have a single ASID if PCID is off and the CR3
+ * write will have flushed it.
+ */
+ if (!cpu_feature_enabled(X86_FEATURE_PCID))
+ return;
+
+ if (!static_cpu_has(X86_FEATURE_PTI))
+ return;
+
+ __set_bit(kern_pcid(asid),
+ (unsigned long *)this_cpu_ptr(&cpu_tlbstate.user_pcid_flush_mask));
+}
+
+static void load_new_mm_cr3(pgd_t *pgdir, u16 new_asid, bool need_flush)
+{
+ unsigned long new_mm_cr3;
+
+ if (need_flush) {
+ invalidate_user_asid(new_asid);
+ new_mm_cr3 = build_cr3(pgdir, new_asid);
+ } else {
+ new_mm_cr3 = build_cr3_noflush(pgdir, new_asid);
+ }
+
+ /*
+ * Caution: many callers of this function expect
+ * that load_cr3() is serializing and orders TLB
+ * fills with respect to the mm_cpumask writes.
+ */
+ write_cr3(new_mm_cr3);
+}
+
+void leave_mm(int cpu)
+{
+ struct mm_struct *loaded_mm = this_cpu_read(cpu_tlbstate.loaded_mm);
+
+ /*
+ * It's plausible that we're in lazy TLB mode while our mm is init_mm.
+ * If so, our callers still expect us to flush the TLB, but there
+ * aren't any user TLB entries in init_mm to worry about.
+ *
+ * This needs to happen before any other sanity checks due to
+ * intel_idle's shenanigans.
+ */
+ if (loaded_mm == &init_mm)
+ return;
+
+ /* Warn if we're not lazy. */
+ WARN_ON(!this_cpu_read(cpu_tlbstate_shared.is_lazy));
+
+ switch_mm(NULL, &init_mm, NULL);
+}
+EXPORT_SYMBOL_GPL(leave_mm);
+
+void switch_mm(struct mm_struct *prev, struct mm_struct *next,
+ struct task_struct *tsk)
+{
+ unsigned long flags;
+
+ local_irq_save(flags);
+ switch_mm_irqs_off(prev, next, tsk);
+ local_irq_restore(flags);
+}
+
+/*
+ * Invoked from return to user/guest by a task that opted-in to L1D
+ * flushing but ended up running on an SMT enabled core due to wrong
+ * affinity settings or CPU hotplug. This is part of the paranoid L1D flush
+ * contract which this task requested.
+ */
+static void l1d_flush_force_sigbus(struct callback_head *ch)
+{
+ force_sig(SIGBUS);
+}
+
+static void l1d_flush_evaluate(unsigned long prev_mm, unsigned long next_mm,
+ struct task_struct *next)
+{
+ /* Flush L1D if the outgoing task requests it */
+ if (prev_mm & LAST_USER_MM_L1D_FLUSH)
+ wrmsrl(MSR_IA32_FLUSH_CMD, L1D_FLUSH);
+
+ /* Check whether the incoming task opted in for L1D flush */
+ if (likely(!(next_mm & LAST_USER_MM_L1D_FLUSH)))
+ return;
+
+ /*
+ * Validate that it is not running on an SMT sibling as this would
+ * make the excercise pointless because the siblings share L1D. If
+ * it runs on a SMT sibling, notify it with SIGBUS on return to
+ * user/guest
+ */
+ if (this_cpu_read(cpu_info.smt_active)) {
+ clear_ti_thread_flag(&next->thread_info, TIF_SPEC_L1D_FLUSH);
+ next->l1d_flush_kill.func = l1d_flush_force_sigbus;
+ task_work_add(next, &next->l1d_flush_kill, TWA_RESUME);
+ }
+}
+
+static unsigned long mm_mangle_tif_spec_bits(struct task_struct *next)
+{
+ unsigned long next_tif = read_task_thread_flags(next);
+ unsigned long spec_bits = (next_tif >> TIF_SPEC_IB) & LAST_USER_MM_SPEC_MASK;
+
+ /*
+ * Ensure that the bit shift above works as expected and the two flags
+ * end up in bit 0 and 1.
+ */
+ BUILD_BUG_ON(TIF_SPEC_L1D_FLUSH != TIF_SPEC_IB + 1);
+
+ return (unsigned long)next->mm | spec_bits;
+}
+
+static void cond_mitigation(struct task_struct *next)
+{
+ unsigned long prev_mm, next_mm;
+
+ if (!next || !next->mm)
+ return;
+
+ next_mm = mm_mangle_tif_spec_bits(next);
+ prev_mm = this_cpu_read(cpu_tlbstate.last_user_mm_spec);
+
+ /*
+ * Avoid user/user BTB poisoning by flushing the branch predictor
+ * when switching between processes. This stops one process from
+ * doing Spectre-v2 attacks on another.
+ *
+ * Both, the conditional and the always IBPB mode use the mm
+ * pointer to avoid the IBPB when switching between tasks of the
+ * same process. Using the mm pointer instead of mm->context.ctx_id
+ * opens a hypothetical hole vs. mm_struct reuse, which is more or
+ * less impossible to control by an attacker. Aside of that it
+ * would only affect the first schedule so the theoretically
+ * exposed data is not really interesting.
+ */
+ if (static_branch_likely(&switch_mm_cond_ibpb)) {
+ /*
+ * This is a bit more complex than the always mode because
+ * it has to handle two cases:
+ *
+ * 1) Switch from a user space task (potential attacker)
+ * which has TIF_SPEC_IB set to a user space task
+ * (potential victim) which has TIF_SPEC_IB not set.
+ *
+ * 2) Switch from a user space task (potential attacker)
+ * which has TIF_SPEC_IB not set to a user space task
+ * (potential victim) which has TIF_SPEC_IB set.
+ *
+ * This could be done by unconditionally issuing IBPB when
+ * a task which has TIF_SPEC_IB set is either scheduled in
+ * or out. Though that results in two flushes when:
+ *
+ * - the same user space task is scheduled out and later
+ * scheduled in again and only a kernel thread ran in
+ * between.
+ *
+ * - a user space task belonging to the same process is
+ * scheduled in after a kernel thread ran in between
+ *
+ * - a user space task belonging to the same process is
+ * scheduled in immediately.
+ *
+ * Optimize this with reasonably small overhead for the
+ * above cases. Mangle the TIF_SPEC_IB bit into the mm
+ * pointer of the incoming task which is stored in
+ * cpu_tlbstate.last_user_mm_spec for comparison.
+ *
+ * Issue IBPB only if the mm's are different and one or
+ * both have the IBPB bit set.
+ */
+ if (next_mm != prev_mm &&
+ (next_mm | prev_mm) & LAST_USER_MM_IBPB)
+ indirect_branch_prediction_barrier();
+ }
+
+ if (static_branch_unlikely(&switch_mm_always_ibpb)) {
+ /*
+ * Only flush when switching to a user space task with a
+ * different context than the user space task which ran
+ * last on this CPU.
+ */
+ if ((prev_mm & ~LAST_USER_MM_SPEC_MASK) !=
+ (unsigned long)next->mm)
+ indirect_branch_prediction_barrier();
+ }
+
+ if (static_branch_unlikely(&switch_mm_cond_l1d_flush)) {
+ /*
+ * Flush L1D when the outgoing task requested it and/or
+ * check whether the incoming task requested L1D flushing
+ * and ended up on an SMT sibling.
+ */
+ if (unlikely((prev_mm | next_mm) & LAST_USER_MM_L1D_FLUSH))
+ l1d_flush_evaluate(prev_mm, next_mm, next);
+ }
+
+ this_cpu_write(cpu_tlbstate.last_user_mm_spec, next_mm);
+}
+
+#ifdef CONFIG_PERF_EVENTS
+static inline void cr4_update_pce_mm(struct mm_struct *mm)
+{
+ if (static_branch_unlikely(&rdpmc_always_available_key) ||
+ (!static_branch_unlikely(&rdpmc_never_available_key) &&
+ atomic_read(&mm->context.perf_rdpmc_allowed))) {
+ /*
+ * Clear the existing dirty counters to
+ * prevent the leak for an RDPMC task.
+ */
+ perf_clear_dirty_counters();
+ cr4_set_bits_irqsoff(X86_CR4_PCE);
+ } else
+ cr4_clear_bits_irqsoff(X86_CR4_PCE);
+}
+
+void cr4_update_pce(void *ignored)
+{
+ cr4_update_pce_mm(this_cpu_read(cpu_tlbstate.loaded_mm));
+}
+
+#else
+static inline void cr4_update_pce_mm(struct mm_struct *mm) { }
+#endif
+
+void switch_mm_irqs_off(struct mm_struct *prev, struct mm_struct *next,
+ struct task_struct *tsk)
+{
+ struct mm_struct *real_prev = this_cpu_read(cpu_tlbstate.loaded_mm);
+ u16 prev_asid = this_cpu_read(cpu_tlbstate.loaded_mm_asid);
+ bool was_lazy = this_cpu_read(cpu_tlbstate_shared.is_lazy);
+ unsigned cpu = smp_processor_id();
+ u64 next_tlb_gen;
+ bool need_flush;
+ u16 new_asid;
+
+ /*
+ * NB: The scheduler will call us with prev == next when switching
+ * from lazy TLB mode to normal mode if active_mm isn't changing.
+ * When this happens, we don't assume that CR3 (and hence
+ * cpu_tlbstate.loaded_mm) matches next.
+ *
+ * NB: leave_mm() calls us with prev == NULL and tsk == NULL.
+ */
+
+ /* We don't want flush_tlb_func() to run concurrently with us. */
+ if (IS_ENABLED(CONFIG_PROVE_LOCKING))
+ WARN_ON_ONCE(!irqs_disabled());
+
+ /*
+ * Verify that CR3 is what we think it is. This will catch
+ * hypothetical buggy code that directly switches to swapper_pg_dir
+ * without going through leave_mm() / switch_mm_irqs_off() or that
+ * does something like write_cr3(read_cr3_pa()).
+ *
+ * Only do this check if CONFIG_DEBUG_VM=y because __read_cr3()
+ * isn't free.
+ */
+#ifdef CONFIG_DEBUG_VM
+ if (WARN_ON_ONCE(__read_cr3() != build_cr3(real_prev->pgd, prev_asid))) {
+ /*
+ * If we were to BUG here, we'd be very likely to kill
+ * the system so hard that we don't see the call trace.
+ * Try to recover instead by ignoring the error and doing
+ * a global flush to minimize the chance of corruption.
+ *
+ * (This is far from being a fully correct recovery.
+ * Architecturally, the CPU could prefetch something
+ * back into an incorrect ASID slot and leave it there
+ * to cause trouble down the road. It's better than
+ * nothing, though.)
+ */
+ __flush_tlb_all();
+ }
+#endif
+ if (was_lazy)
+ this_cpu_write(cpu_tlbstate_shared.is_lazy, false);
+
+ /*
+ * The membarrier system call requires a full memory barrier and
+ * core serialization before returning to user-space, after
+ * storing to rq->curr, when changing mm. This is because
+ * membarrier() sends IPIs to all CPUs that are in the target mm
+ * to make them issue memory barriers. However, if another CPU
+ * switches to/from the target mm concurrently with
+ * membarrier(), it can cause that CPU not to receive an IPI
+ * when it really should issue a memory barrier. Writing to CR3
+ * provides that full memory barrier and core serializing
+ * instruction.
+ */
+ if (real_prev == next) {
+ VM_WARN_ON(this_cpu_read(cpu_tlbstate.ctxs[prev_asid].ctx_id) !=
+ next->context.ctx_id);
+
+ /*
+ * Even in lazy TLB mode, the CPU should stay set in the
+ * mm_cpumask. The TLB shootdown code can figure out from
+ * cpu_tlbstate_shared.is_lazy whether or not to send an IPI.
+ */
+ if (WARN_ON_ONCE(real_prev != &init_mm &&
+ !cpumask_test_cpu(cpu, mm_cpumask(next))))
+ cpumask_set_cpu(cpu, mm_cpumask(next));
+
+ /*
+ * If the CPU is not in lazy TLB mode, we are just switching
+ * from one thread in a process to another thread in the same
+ * process. No TLB flush required.
+ */
+ if (!was_lazy)
+ return;
+
+ /*
+ * Read the tlb_gen to check whether a flush is needed.
+ * If the TLB is up to date, just use it.
+ * The barrier synchronizes with the tlb_gen increment in
+ * the TLB shootdown code.
+ */
+ smp_mb();
+ next_tlb_gen = atomic64_read(&next->context.tlb_gen);
+ if (this_cpu_read(cpu_tlbstate.ctxs[prev_asid].tlb_gen) ==
+ next_tlb_gen)
+ return;
+
+ /*
+ * TLB contents went out of date while we were in lazy
+ * mode. Fall through to the TLB switching code below.
+ */
+ new_asid = prev_asid;
+ need_flush = true;
+ } else {
+ /*
+ * Apply process to process speculation vulnerability
+ * mitigations if applicable.
+ */
+ cond_mitigation(tsk);
+
+ /*
+ * Stop remote flushes for the previous mm.
+ * Skip kernel threads; we never send init_mm TLB flushing IPIs,
+ * but the bitmap manipulation can cause cache line contention.
+ */
+ if (real_prev != &init_mm) {
+ VM_WARN_ON_ONCE(!cpumask_test_cpu(cpu,
+ mm_cpumask(real_prev)));
+ cpumask_clear_cpu(cpu, mm_cpumask(real_prev));
+ }
+
+ /*
+ * Start remote flushes and then read tlb_gen.
+ */
+ if (next != &init_mm)
+ cpumask_set_cpu(cpu, mm_cpumask(next));
+ next_tlb_gen = atomic64_read(&next->context.tlb_gen);
+
+ choose_new_asid(next, next_tlb_gen, &new_asid, &need_flush);
+
+ /* Let nmi_uaccess_okay() know that we're changing CR3. */
+ this_cpu_write(cpu_tlbstate.loaded_mm, LOADED_MM_SWITCHING);
+ barrier();
+ }
+
+ if (need_flush) {
+ this_cpu_write(cpu_tlbstate.ctxs[new_asid].ctx_id, next->context.ctx_id);
+ this_cpu_write(cpu_tlbstate.ctxs[new_asid].tlb_gen, next_tlb_gen);
+ load_new_mm_cr3(next->pgd, new_asid, true);
+
+ trace_tlb_flush(TLB_FLUSH_ON_TASK_SWITCH, TLB_FLUSH_ALL);
+ } else {
+ /* The new ASID is already up to date. */
+ load_new_mm_cr3(next->pgd, new_asid, false);
+
+ trace_tlb_flush(TLB_FLUSH_ON_TASK_SWITCH, 0);
+ }
+
+ /* Make sure we write CR3 before loaded_mm. */
+ barrier();
+
+ this_cpu_write(cpu_tlbstate.loaded_mm, next);
+ this_cpu_write(cpu_tlbstate.loaded_mm_asid, new_asid);
+
+ if (next != real_prev) {
+ cr4_update_pce_mm(next);
+ switch_ldt(real_prev, next);
+ }
+}
+
+/*
+ * Please ignore the name of this function. It should be called
+ * switch_to_kernel_thread().
+ *
+ * enter_lazy_tlb() is a hint from the scheduler that we are entering a
+ * kernel thread or other context without an mm. Acceptable implementations
+ * include doing nothing whatsoever, switching to init_mm, or various clever
+ * lazy tricks to try to minimize TLB flushes.
+ *
+ * The scheduler reserves the right to call enter_lazy_tlb() several times
+ * in a row. It will notify us that we're going back to a real mm by
+ * calling switch_mm_irqs_off().
+ */
+void enter_lazy_tlb(struct mm_struct *mm, struct task_struct *tsk)
+{
+ if (this_cpu_read(cpu_tlbstate.loaded_mm) == &init_mm)
+ return;
+
+ this_cpu_write(cpu_tlbstate_shared.is_lazy, true);
+}
+
+/*
+ * Call this when reinitializing a CPU. It fixes the following potential
+ * problems:
+ *
+ * - The ASID changed from what cpu_tlbstate thinks it is (most likely
+ * because the CPU was taken down and came back up with CR3's PCID
+ * bits clear. CPU hotplug can do this.
+ *
+ * - The TLB contains junk in slots corresponding to inactive ASIDs.
+ *
+ * - The CPU went so far out to lunch that it may have missed a TLB
+ * flush.
+ */
+void initialize_tlbstate_and_flush(void)
+{
+ int i;
+ struct mm_struct *mm = this_cpu_read(cpu_tlbstate.loaded_mm);
+ u64 tlb_gen = atomic64_read(&init_mm.context.tlb_gen);
+ unsigned long cr3 = __read_cr3();
+
+ /* Assert that CR3 already references the right mm. */
+ WARN_ON((cr3 & CR3_ADDR_MASK) != __pa(mm->pgd));
+
+ /*
+ * Assert that CR4.PCIDE is set if needed. (CR4.PCIDE initialization
+ * doesn't work like other CR4 bits because it can only be set from
+ * long mode.)
+ */
+ WARN_ON(boot_cpu_has(X86_FEATURE_PCID) &&
+ !(cr4_read_shadow() & X86_CR4_PCIDE));
+
+ /* Force ASID 0 and force a TLB flush. */
+ write_cr3(build_cr3(mm->pgd, 0));
+
+ /* Reinitialize tlbstate. */
+ this_cpu_write(cpu_tlbstate.last_user_mm_spec, LAST_USER_MM_INIT);
+ this_cpu_write(cpu_tlbstate.loaded_mm_asid, 0);
+ this_cpu_write(cpu_tlbstate.next_asid, 1);
+ this_cpu_write(cpu_tlbstate.ctxs[0].ctx_id, mm->context.ctx_id);
+ this_cpu_write(cpu_tlbstate.ctxs[0].tlb_gen, tlb_gen);
+
+ for (i = 1; i < TLB_NR_DYN_ASIDS; i++)
+ this_cpu_write(cpu_tlbstate.ctxs[i].ctx_id, 0);
+}
+
+/*
+ * flush_tlb_func()'s memory ordering requirement is that any
+ * TLB fills that happen after we flush the TLB are ordered after we
+ * read active_mm's tlb_gen. We don't need any explicit barriers
+ * because all x86 flush operations are serializing and the
+ * atomic64_read operation won't be reordered by the compiler.
+ */
+static void flush_tlb_func(void *info)
+{
+ /*
+ * We have three different tlb_gen values in here. They are:
+ *
+ * - mm_tlb_gen: the latest generation.
+ * - local_tlb_gen: the generation that this CPU has already caught
+ * up to.
+ * - f->new_tlb_gen: the generation that the requester of the flush
+ * wants us to catch up to.
+ */
+ const struct flush_tlb_info *f = info;
+ struct mm_struct *loaded_mm = this_cpu_read(cpu_tlbstate.loaded_mm);
+ u32 loaded_mm_asid = this_cpu_read(cpu_tlbstate.loaded_mm_asid);
+ u64 local_tlb_gen = this_cpu_read(cpu_tlbstate.ctxs[loaded_mm_asid].tlb_gen);
+ bool local = smp_processor_id() == f->initiating_cpu;
+ unsigned long nr_invalidate = 0;
+ u64 mm_tlb_gen;
+
+ /* This code cannot presently handle being reentered. */
+ VM_WARN_ON(!irqs_disabled());
+
+ if (!local) {
+ inc_irq_stat(irq_tlb_count);
+ count_vm_tlb_event(NR_TLB_REMOTE_FLUSH_RECEIVED);
+
+ /* Can only happen on remote CPUs */
+ if (f->mm && f->mm != loaded_mm)
+ return;
+ }
+
+ if (unlikely(loaded_mm == &init_mm))
+ return;
+
+ VM_WARN_ON(this_cpu_read(cpu_tlbstate.ctxs[loaded_mm_asid].ctx_id) !=
+ loaded_mm->context.ctx_id);
+
+ if (this_cpu_read(cpu_tlbstate_shared.is_lazy)) {
+ /*
+ * We're in lazy mode. We need to at least flush our
+ * paging-structure cache to avoid speculatively reading
+ * garbage into our TLB. Since switching to init_mm is barely
+ * slower than a minimal flush, just switch to init_mm.
+ *
+ * This should be rare, with native_flush_tlb_multi() skipping
+ * IPIs to lazy TLB mode CPUs.
+ */
+ switch_mm_irqs_off(NULL, &init_mm, NULL);
+ return;
+ }
+
+ if (unlikely(f->new_tlb_gen != TLB_GENERATION_INVALID &&
+ f->new_tlb_gen <= local_tlb_gen)) {
+ /*
+ * The TLB is already up to date in respect to f->new_tlb_gen.
+ * While the core might be still behind mm_tlb_gen, checking
+ * mm_tlb_gen unnecessarily would have negative caching effects
+ * so avoid it.
+ */
+ return;
+ }
+
+ /*
+ * Defer mm_tlb_gen reading as long as possible to avoid cache
+ * contention.
+ */
+ mm_tlb_gen = atomic64_read(&loaded_mm->context.tlb_gen);
+
+ if (unlikely(local_tlb_gen == mm_tlb_gen)) {
+ /*
+ * There's nothing to do: we're already up to date. This can
+ * happen if two concurrent flushes happen -- the first flush to
+ * be handled can catch us all the way up, leaving no work for
+ * the second flush.
+ */
+ goto done;
+ }
+
+ WARN_ON_ONCE(local_tlb_gen > mm_tlb_gen);
+ WARN_ON_ONCE(f->new_tlb_gen > mm_tlb_gen);
+
+ /*
+ * If we get to this point, we know that our TLB is out of date.
+ * This does not strictly imply that we need to flush (it's
+ * possible that f->new_tlb_gen <= local_tlb_gen), but we're
+ * going to need to flush in the very near future, so we might
+ * as well get it over with.
+ *
+ * The only question is whether to do a full or partial flush.
+ *
+ * We do a partial flush if requested and two extra conditions
+ * are met:
+ *
+ * 1. f->new_tlb_gen == local_tlb_gen + 1. We have an invariant that
+ * we've always done all needed flushes to catch up to
+ * local_tlb_gen. If, for example, local_tlb_gen == 2 and
+ * f->new_tlb_gen == 3, then we know that the flush needed to bring
+ * us up to date for tlb_gen 3 is the partial flush we're
+ * processing.
+ *
+ * As an example of why this check is needed, suppose that there
+ * are two concurrent flushes. The first is a full flush that
+ * changes context.tlb_gen from 1 to 2. The second is a partial
+ * flush that changes context.tlb_gen from 2 to 3. If they get
+ * processed on this CPU in reverse order, we'll see
+ * local_tlb_gen == 1, mm_tlb_gen == 3, and end != TLB_FLUSH_ALL.
+ * If we were to use __flush_tlb_one_user() and set local_tlb_gen to
+ * 3, we'd be break the invariant: we'd update local_tlb_gen above
+ * 1 without the full flush that's needed for tlb_gen 2.
+ *
+ * 2. f->new_tlb_gen == mm_tlb_gen. This is purely an optimization.
+ * Partial TLB flushes are not all that much cheaper than full TLB
+ * flushes, so it seems unlikely that it would be a performance win
+ * to do a partial flush if that won't bring our TLB fully up to
+ * date. By doing a full flush instead, we can increase
+ * local_tlb_gen all the way to mm_tlb_gen and we can probably
+ * avoid another flush in the very near future.
+ */
+ if (f->end != TLB_FLUSH_ALL &&
+ f->new_tlb_gen == local_tlb_gen + 1 &&
+ f->new_tlb_gen == mm_tlb_gen) {
+ /* Partial flush */
+ unsigned long addr = f->start;
+
+ /* Partial flush cannot have invalid generations */
+ VM_WARN_ON(f->new_tlb_gen == TLB_GENERATION_INVALID);
+
+ /* Partial flush must have valid mm */
+ VM_WARN_ON(f->mm == NULL);
+
+ nr_invalidate = (f->end - f->start) >> f->stride_shift;
+
+ while (addr < f->end) {
+ flush_tlb_one_user(addr);
+ addr += 1UL << f->stride_shift;
+ }
+ if (local)
+ count_vm_tlb_events(NR_TLB_LOCAL_FLUSH_ONE, nr_invalidate);
+ } else {
+ /* Full flush. */
+ nr_invalidate = TLB_FLUSH_ALL;
+
+ flush_tlb_local();
+ if (local)
+ count_vm_tlb_event(NR_TLB_LOCAL_FLUSH_ALL);
+ }
+
+ /* Both paths above update our state to mm_tlb_gen. */
+ this_cpu_write(cpu_tlbstate.ctxs[loaded_mm_asid].tlb_gen, mm_tlb_gen);
+
+ /* Tracing is done in a unified manner to reduce the code size */
+done:
+ trace_tlb_flush(!local ? TLB_REMOTE_SHOOTDOWN :
+ (f->mm == NULL) ? TLB_LOCAL_SHOOTDOWN :
+ TLB_LOCAL_MM_SHOOTDOWN,
+ nr_invalidate);
+}
+
+static bool tlb_is_not_lazy(int cpu, void *data)
+{
+ return !per_cpu(cpu_tlbstate_shared.is_lazy, cpu);
+}
+
+DEFINE_PER_CPU_SHARED_ALIGNED(struct tlb_state_shared, cpu_tlbstate_shared);
+EXPORT_PER_CPU_SYMBOL(cpu_tlbstate_shared);
+
+STATIC_NOPV void native_flush_tlb_multi(const struct cpumask *cpumask,
+ const struct flush_tlb_info *info)
+{
+ /*
+ * Do accounting and tracing. Note that there are (and have always been)
+ * cases in which a remote TLB flush will be traced, but eventually
+ * would not happen.
+ */
+ count_vm_tlb_event(NR_TLB_REMOTE_FLUSH);
+ if (info->end == TLB_FLUSH_ALL)
+ trace_tlb_flush(TLB_REMOTE_SEND_IPI, TLB_FLUSH_ALL);
+ else
+ trace_tlb_flush(TLB_REMOTE_SEND_IPI,
+ (info->end - info->start) >> PAGE_SHIFT);
+
+ /*
+ * If no page tables were freed, we can skip sending IPIs to
+ * CPUs in lazy TLB mode. They will flush the CPU themselves
+ * at the next context switch.
+ *
+ * However, if page tables are getting freed, we need to send the
+ * IPI everywhere, to prevent CPUs in lazy TLB mode from tripping
+ * up on the new contents of what used to be page tables, while
+ * doing a speculative memory access.
+ */
+ if (info->freed_tables)
+ on_each_cpu_mask(cpumask, flush_tlb_func, (void *)info, true);
+ else
+ on_each_cpu_cond_mask(tlb_is_not_lazy, flush_tlb_func,
+ (void *)info, 1, cpumask);
+}
+
+void flush_tlb_multi(const struct cpumask *cpumask,
+ const struct flush_tlb_info *info)
+{
+ __flush_tlb_multi(cpumask, info);
+}
+
+/*
+ * See Documentation/x86/tlb.rst for details. We choose 33
+ * because it is large enough to cover the vast majority (at
+ * least 95%) of allocations, and is small enough that we are
+ * confident it will not cause too much overhead. Each single
+ * flush is about 100 ns, so this caps the maximum overhead at
+ * _about_ 3,000 ns.
+ *
+ * This is in units of pages.
+ */
+unsigned long tlb_single_page_flush_ceiling __read_mostly = 33;
+
+static DEFINE_PER_CPU_SHARED_ALIGNED(struct flush_tlb_info, flush_tlb_info);
+
+#ifdef CONFIG_DEBUG_VM
+static DEFINE_PER_CPU(unsigned int, flush_tlb_info_idx);
+#endif
+
+static struct flush_tlb_info *get_flush_tlb_info(struct mm_struct *mm,
+ unsigned long start, unsigned long end,
+ unsigned int stride_shift, bool freed_tables,
+ u64 new_tlb_gen)
+{
+ struct flush_tlb_info *info = this_cpu_ptr(&flush_tlb_info);
+
+#ifdef CONFIG_DEBUG_VM
+ /*
+ * Ensure that the following code is non-reentrant and flush_tlb_info
+ * is not overwritten. This means no TLB flushing is initiated by
+ * interrupt handlers and machine-check exception handlers.
+ */
+ BUG_ON(this_cpu_inc_return(flush_tlb_info_idx) != 1);
+#endif
+
+ info->start = start;
+ info->end = end;
+ info->mm = mm;
+ info->stride_shift = stride_shift;
+ info->freed_tables = freed_tables;
+ info->new_tlb_gen = new_tlb_gen;
+ info->initiating_cpu = smp_processor_id();
+
+ return info;
+}
+
+static void put_flush_tlb_info(void)
+{
+#ifdef CONFIG_DEBUG_VM
+ /* Complete reentrancy prevention checks */
+ barrier();
+ this_cpu_dec(flush_tlb_info_idx);
+#endif
+}
+
+void flush_tlb_mm_range(struct mm_struct *mm, unsigned long start,
+ unsigned long end, unsigned int stride_shift,
+ bool freed_tables)
+{
+ struct flush_tlb_info *info;
+ u64 new_tlb_gen;
+ int cpu;
+
+ cpu = get_cpu();
+
+ /* Should we flush just the requested range? */
+ if ((end == TLB_FLUSH_ALL) ||
+ ((end - start) >> stride_shift) > tlb_single_page_flush_ceiling) {
+ start = 0;
+ end = TLB_FLUSH_ALL;
+ }
+
+ /* This is also a barrier that synchronizes with switch_mm(). */
+ new_tlb_gen = inc_mm_tlb_gen(mm);
+
+ info = get_flush_tlb_info(mm, start, end, stride_shift, freed_tables,
+ new_tlb_gen);
+
+ /*
+ * flush_tlb_multi() is not optimized for the common case in which only
+ * a local TLB flush is needed. Optimize this use-case by calling
+ * flush_tlb_func_local() directly in this case.
+ */
+ if (cpumask_any_but(mm_cpumask(mm), cpu) < nr_cpu_ids) {
+ flush_tlb_multi(mm_cpumask(mm), info);
+ } else if (mm == this_cpu_read(cpu_tlbstate.loaded_mm)) {
+ lockdep_assert_irqs_enabled();
+ local_irq_disable();
+ flush_tlb_func(info);
+ local_irq_enable();
+ }
+
+ put_flush_tlb_info();
+ put_cpu();
+}
+
+
+static void do_flush_tlb_all(void *info)
+{
+ count_vm_tlb_event(NR_TLB_REMOTE_FLUSH_RECEIVED);
+ __flush_tlb_all();
+}
+
+void flush_tlb_all(void)
+{
+ count_vm_tlb_event(NR_TLB_REMOTE_FLUSH);
+ on_each_cpu(do_flush_tlb_all, NULL, 1);
+}
+
+static void do_kernel_range_flush(void *info)
+{
+ struct flush_tlb_info *f = info;
+ unsigned long addr;
+
+ /* flush range by one by one 'invlpg' */
+ for (addr = f->start; addr < f->end; addr += PAGE_SIZE)
+ flush_tlb_one_kernel(addr);
+}
+
+void flush_tlb_kernel_range(unsigned long start, unsigned long end)
+{
+ /* Balance as user space task's flush, a bit conservative */
+ if (end == TLB_FLUSH_ALL ||
+ (end - start) > tlb_single_page_flush_ceiling << PAGE_SHIFT) {
+ on_each_cpu(do_flush_tlb_all, NULL, 1);
+ } else {
+ struct flush_tlb_info *info;
+
+ preempt_disable();
+ info = get_flush_tlb_info(NULL, start, end, 0, false,
+ TLB_GENERATION_INVALID);
+
+ on_each_cpu(do_kernel_range_flush, info, 1);
+
+ put_flush_tlb_info();
+ preempt_enable();
+ }
+}
+
+/*
+ * This can be used from process context to figure out what the value of
+ * CR3 is without needing to do a (slow) __read_cr3().
+ *
+ * It's intended to be used for code like KVM that sneakily changes CR3
+ * and needs to restore it. It needs to be used very carefully.
+ */
+unsigned long __get_current_cr3_fast(void)
+{
+ unsigned long cr3 = build_cr3(this_cpu_read(cpu_tlbstate.loaded_mm)->pgd,
+ this_cpu_read(cpu_tlbstate.loaded_mm_asid));
+
+ /* For now, be very restrictive about when this can be called. */
+ VM_WARN_ON(in_nmi() || preemptible());
+
+ VM_BUG_ON(cr3 != __read_cr3());
+ return cr3;
+}
+EXPORT_SYMBOL_GPL(__get_current_cr3_fast);
+
+/*
+ * Flush one page in the kernel mapping
+ */
+void flush_tlb_one_kernel(unsigned long addr)
+{
+ count_vm_tlb_event(NR_TLB_LOCAL_FLUSH_ONE);
+
+ /*
+ * If PTI is off, then __flush_tlb_one_user() is just INVLPG or its
+ * paravirt equivalent. Even with PCID, this is sufficient: we only
+ * use PCID if we also use global PTEs for the kernel mapping, and
+ * INVLPG flushes global translations across all address spaces.
+ *
+ * If PTI is on, then the kernel is mapped with non-global PTEs, and
+ * __flush_tlb_one_user() will flush the given address for the current
+ * kernel address space and for its usermode counterpart, but it does
+ * not flush it for other address spaces.
+ */
+ flush_tlb_one_user(addr);
+
+ if (!static_cpu_has(X86_FEATURE_PTI))
+ return;
+
+ /*
+ * See above. We need to propagate the flush to all other address
+ * spaces. In principle, we only need to propagate it to kernelmode
+ * address spaces, but the extra bookkeeping we would need is not
+ * worth it.
+ */
+ this_cpu_write(cpu_tlbstate.invalidate_other, true);
+}
+
+/*
+ * Flush one page in the user mapping
+ */
+STATIC_NOPV void native_flush_tlb_one_user(unsigned long addr)
+{
+ u32 loaded_mm_asid = this_cpu_read(cpu_tlbstate.loaded_mm_asid);
+
+ asm volatile("invlpg (%0)" ::"r" (addr) : "memory");
+
+ if (!static_cpu_has(X86_FEATURE_PTI))
+ return;
+
+ /*
+ * Some platforms #GP if we call invpcid(type=1/2) before CR4.PCIDE=1.
+ * Just use invalidate_user_asid() in case we are called early.
+ */
+ if (!this_cpu_has(X86_FEATURE_INVPCID_SINGLE))
+ invalidate_user_asid(loaded_mm_asid);
+ else
+ invpcid_flush_one(user_pcid(loaded_mm_asid), addr);
+}
+
+void flush_tlb_one_user(unsigned long addr)
+{
+ __flush_tlb_one_user(addr);
+}
+
+/*
+ * Flush everything
+ */
+STATIC_NOPV void native_flush_tlb_global(void)
+{
+ unsigned long flags;
+
+ if (static_cpu_has(X86_FEATURE_INVPCID)) {
+ /*
+ * Using INVPCID is considerably faster than a pair of writes
+ * to CR4 sandwiched inside an IRQ flag save/restore.
+ *
+ * Note, this works with CR4.PCIDE=0 or 1.
+ */
+ invpcid_flush_all();
+ return;
+ }
+
+ /*
+ * Read-modify-write to CR4 - protect it from preemption and
+ * from interrupts. (Use the raw variant because this code can
+ * be called from deep inside debugging code.)
+ */
+ raw_local_irq_save(flags);
+
+ __native_tlb_flush_global(this_cpu_read(cpu_tlbstate.cr4));
+
+ raw_local_irq_restore(flags);
+}
+
+/*
+ * Flush the entire current user mapping
+ */
+STATIC_NOPV void native_flush_tlb_local(void)
+{
+ /*
+ * Preemption or interrupts must be disabled to protect the access
+ * to the per CPU variable and to prevent being preempted between
+ * read_cr3() and write_cr3().
+ */
+ WARN_ON_ONCE(preemptible());
+
+ invalidate_user_asid(this_cpu_read(cpu_tlbstate.loaded_mm_asid));
+
+ /* If current->mm == NULL then the read_cr3() "borrows" an mm */
+ native_write_cr3(__native_read_cr3());
+}
+
+void flush_tlb_local(void)
+{
+ __flush_tlb_local();
+}
+
+/*
+ * Flush everything
+ */
+void __flush_tlb_all(void)
+{
+ /*
+ * This is to catch users with enabled preemption and the PGE feature
+ * and don't trigger the warning in __native_flush_tlb().
+ */
+ VM_WARN_ON_ONCE(preemptible());
+
+ if (boot_cpu_has(X86_FEATURE_PGE)) {
+ __flush_tlb_global();
+ } else {
+ /*
+ * !PGE -> !PCID (setup_pcid()), thus every flush is total.
+ */
+ flush_tlb_local();
+ }
+}
+EXPORT_SYMBOL_GPL(__flush_tlb_all);
+
+void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch)
+{
+ struct flush_tlb_info *info;
+
+ int cpu = get_cpu();
+
+ info = get_flush_tlb_info(NULL, 0, TLB_FLUSH_ALL, 0, false,
+ TLB_GENERATION_INVALID);
+ /*
+ * flush_tlb_multi() is not optimized for the common case in which only
+ * a local TLB flush is needed. Optimize this use-case by calling
+ * flush_tlb_func_local() directly in this case.
+ */
+ if (cpumask_any_but(&batch->cpumask, cpu) < nr_cpu_ids) {
+ flush_tlb_multi(&batch->cpumask, info);
+ } else if (cpumask_test_cpu(cpu, &batch->cpumask)) {
+ lockdep_assert_irqs_enabled();
+ local_irq_disable();
+ flush_tlb_func(info);
+ local_irq_enable();
+ }
+
+ cpumask_clear(&batch->cpumask);
+
+ put_flush_tlb_info();
+ put_cpu();
+}
+
+/*
+ * Blindly accessing user memory from NMI context can be dangerous
+ * if we're in the middle of switching the current user task or
+ * switching the loaded mm. It can also be dangerous if we
+ * interrupted some kernel code that was temporarily using a
+ * different mm.
+ */
+bool nmi_uaccess_okay(void)
+{
+ struct mm_struct *loaded_mm = this_cpu_read(cpu_tlbstate.loaded_mm);
+ struct mm_struct *current_mm = current->mm;
+
+ VM_WARN_ON_ONCE(!loaded_mm);
+
+ /*
+ * The condition we want to check is
+ * current_mm->pgd == __va(read_cr3_pa()). This may be slow, though,
+ * if we're running in a VM with shadow paging, and nmi_uaccess_okay()
+ * is supposed to be reasonably fast.
+ *
+ * Instead, we check the almost equivalent but somewhat conservative
+ * condition below, and we rely on the fact that switch_mm_irqs_off()
+ * sets loaded_mm to LOADED_MM_SWITCHING before writing to CR3.
+ */
+ if (loaded_mm != current_mm)
+ return false;
+
+ VM_WARN_ON_ONCE(current_mm->pgd != __va(read_cr3_pa()));
+
+ return true;
+}
+
+static ssize_t tlbflush_read_file(struct file *file, char __user *user_buf,
+ size_t count, loff_t *ppos)
+{
+ char buf[32];
+ unsigned int len;
+
+ len = sprintf(buf, "%ld\n", tlb_single_page_flush_ceiling);
+ return simple_read_from_buffer(user_buf, count, ppos, buf, len);
+}
+
+static ssize_t tlbflush_write_file(struct file *file,
+ const char __user *user_buf, size_t count, loff_t *ppos)
+{
+ char buf[32];
+ ssize_t len;
+ int ceiling;
+
+ len = min(count, sizeof(buf) - 1);
+ if (copy_from_user(buf, user_buf, len))
+ return -EFAULT;
+
+ buf[len] = '\0';
+ if (kstrtoint(buf, 0, &ceiling))
+ return -EINVAL;
+
+ if (ceiling < 0)
+ return -EINVAL;
+
+ tlb_single_page_flush_ceiling = ceiling;
+ return count;
+}
+
+static const struct file_operations fops_tlbflush = {
+ .read = tlbflush_read_file,
+ .write = tlbflush_write_file,
+ .llseek = default_llseek,
+};
+
+static int __init create_tlb_single_page_flush_ceiling(void)
+{
+ debugfs_create_file("tlb_single_page_flush_ceiling", S_IRUSR | S_IWUSR,
+ arch_debugfs_dir, NULL, &fops_tlbflush);
+ return 0;
+}
+late_initcall(create_tlb_single_page_flush_ceiling);