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Diffstat (limited to '')
| -rw-r--r-- | arch/x86/mm/tlb.c | 1229 |
1 files changed, 1229 insertions, 0 deletions
diff --git a/arch/x86/mm/tlb.c b/arch/x86/mm/tlb.c new file mode 100644 index 000000000..569ac1d57 --- /dev/null +++ b/arch/x86/mm/tlb.c @@ -0,0 +1,1229 @@ +// 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 <asm/tlbflush.h> +#include <asm/mmu_context.h> +#include <asm/nospec-branch.h> +#include <asm/cache.h> +#include <asm/apic.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_others(msk, info) native_flush_tlb_others(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 + */ + +/* + * Use bit 0 to mangle the TIF_SPEC_IB state into the mm pointer which is + * stored in cpu_tlb_state.last_user_mm_ibpb. + */ +#define LAST_USER_MM_IBPB 0x1UL + +/* + * 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 confict 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.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); +} + +static inline unsigned long mm_mangle_tif_spec_ib(struct task_struct *next) +{ + unsigned long next_tif = task_thread_info(next)->flags; + unsigned long ibpb = (next_tif >> TIF_SPEC_IB) & LAST_USER_MM_IBPB; + + return (unsigned long)next->mm | ibpb; +} + +static void cond_ibpb(struct task_struct *next) +{ + if (!next || !next->mm) + return; + + /* + * 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)) { + unsigned long prev_mm, next_mm; + + /* + * 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_ibpb for comparison. + */ + next_mm = mm_mangle_tif_spec_ib(next); + prev_mm = this_cpu_read(cpu_tlbstate.last_user_mm_ibpb); + + /* + * 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(); + + this_cpu_write(cpu_tlbstate.last_user_mm_ibpb, next_mm); + } + + 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 (this_cpu_read(cpu_tlbstate.last_user_mm) != next->mm) { + indirect_branch_prediction_barrier(); + this_cpu_write(cpu_tlbstate.last_user_mm, 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))) + 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.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 + this_cpu_write(cpu_tlbstate.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 + * from cpu_tlbstate.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 { + /* + * 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. + */ + cond_ibpb(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.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_ibpb, LAST_USER_MM_IBPB); + 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_common()'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_common(const struct flush_tlb_info *f, + bool local, enum tlb_flush_reason reason) +{ + /* + * 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. + */ + 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 mm_tlb_gen = atomic64_read(&loaded_mm->context.tlb_gen); + u64 local_tlb_gen = this_cpu_read(cpu_tlbstate.ctxs[loaded_mm_asid].tlb_gen); + + /* This code cannot presently handle being reentered. */ + VM_WARN_ON(!irqs_disabled()); + + 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.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_others skipping + * IPIs to lazy TLB mode CPUs. + */ + switch_mm_irqs_off(NULL, &init_mm, NULL); + return; + } + + 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. + */ + trace_tlb_flush(reason, 0); + return; + } + + 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 optimiation. + * 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 nr_invalidate = (f->end - f->start) >> f->stride_shift; + unsigned long addr = f->start; + + 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); + trace_tlb_flush(reason, nr_invalidate); + } else { + /* Full flush. */ + flush_tlb_local(); + if (local) + count_vm_tlb_event(NR_TLB_LOCAL_FLUSH_ALL); + trace_tlb_flush(reason, TLB_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); +} + +static void flush_tlb_func_local(const void *info, enum tlb_flush_reason reason) +{ + const struct flush_tlb_info *f = info; + + flush_tlb_func_common(f, true, reason); +} + +static void flush_tlb_func_remote(void *info) +{ + const struct flush_tlb_info *f = info; + + inc_irq_stat(irq_tlb_count); + + if (f->mm && f->mm != this_cpu_read(cpu_tlbstate.loaded_mm)) + return; + + count_vm_tlb_event(NR_TLB_REMOTE_FLUSH_RECEIVED); + flush_tlb_func_common(f, false, TLB_REMOTE_SHOOTDOWN); +} + +static bool tlb_is_not_lazy(int cpu, void *data) +{ + return !per_cpu(cpu_tlbstate.is_lazy, cpu); +} + +STATIC_NOPV void native_flush_tlb_others(const struct cpumask *cpumask, + const struct flush_tlb_info *info) +{ + 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) + smp_call_function_many(cpumask, flush_tlb_func_remote, + (void *)info, 1); + else + on_each_cpu_cond_mask(tlb_is_not_lazy, flush_tlb_func_remote, + (void *)info, 1, cpumask); +} + +void flush_tlb_others(const struct cpumask *cpumask, + const struct flush_tlb_info *info) +{ + __flush_tlb_others(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 inline 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; + + return info; +} + +static inline void put_flush_tlb_info(void) +{ +#ifdef CONFIG_DEBUG_VM + /* Complete reentrency 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); + + if (mm == this_cpu_read(cpu_tlbstate.loaded_mm)) { + lockdep_assert_irqs_enabled(); + local_irq_disable(); + flush_tlb_func_local(info, TLB_LOCAL_MM_SHOOTDOWN); + local_irq_enable(); + } + + if (cpumask_any_but(mm_cpumask(mm), cpu) < nr_cpu_ids) + flush_tlb_others(mm_cpumask(mm), info); + + 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, 0); + + 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 cr4, 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); + + cr4 = this_cpu_read(cpu_tlbstate.cr4); + /* toggle PGE */ + native_write_cr4(cr4 ^ X86_CR4_PGE); + /* write old PGE again and flush TLBs */ + native_write_cr4(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); + +/* + * arch_tlbbatch_flush() performs a full TLB flush regardless of the active mm. + * This means that the 'struct flush_tlb_info' that describes which mappings to + * flush is actually fixed. We therefore set a single fixed struct and use it in + * arch_tlbbatch_flush(). + */ +static const struct flush_tlb_info full_flush_tlb_info = { + .mm = NULL, + .start = 0, + .end = TLB_FLUSH_ALL, +}; + +void arch_tlbbatch_flush(struct arch_tlbflush_unmap_batch *batch) +{ + int cpu = get_cpu(); + + if (cpumask_test_cpu(cpu, &batch->cpumask)) { + lockdep_assert_irqs_enabled(); + local_irq_disable(); + flush_tlb_func_local(&full_flush_tlb_info, TLB_LOCAL_SHOOTDOWN); + local_irq_enable(); + } + + if (cpumask_any_but(&batch->cpumask, cpu) < nr_cpu_ids) + flush_tlb_others(&batch->cpumask, &full_flush_tlb_info); + + cpumask_clear(&batch->cpumask); + + 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); |