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-rw-r--r--arch/x86/kernel/traps.c78
1 files changed, 70 insertions, 8 deletions
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index c3b2f863ac..4fa0b17e50 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -51,6 +51,7 @@
#include <asm/ftrace.h>
#include <asm/traps.h>
#include <asm/desc.h>
+#include <asm/fred.h>
#include <asm/fpu/api.h>
#include <asm/cpu.h>
#include <asm/cpu_entry_area.h>
@@ -773,7 +774,7 @@ DEFINE_IDTENTRY_RAW(exc_int3)
*/
asmlinkage __visible noinstr struct pt_regs *sync_regs(struct pt_regs *eregs)
{
- struct pt_regs *regs = (struct pt_regs *)this_cpu_read(pcpu_hot.top_of_stack) - 1;
+ struct pt_regs *regs = (struct pt_regs *)current_top_of_stack() - 1;
if (regs != eregs)
*regs = *eregs;
return regs;
@@ -791,7 +792,7 @@ asmlinkage __visible noinstr struct pt_regs *vc_switch_off_ist(struct pt_regs *r
* trust it and switch to the current kernel stack
*/
if (ip_within_syscall_gap(regs)) {
- sp = this_cpu_read(pcpu_hot.top_of_stack);
+ sp = current_top_of_stack();
goto sync;
}
@@ -935,8 +936,7 @@ static bool notify_debug(struct pt_regs *regs, unsigned long *dr6)
return false;
}
-static __always_inline void exc_debug_kernel(struct pt_regs *regs,
- unsigned long dr6)
+static noinstr void exc_debug_kernel(struct pt_regs *regs, unsigned long dr6)
{
/*
* Disable breakpoints during exception handling; recursive exceptions
@@ -948,6 +948,11 @@ static __always_inline void exc_debug_kernel(struct pt_regs *regs,
*
* Entry text is excluded for HW_BP_X and cpu_entry_area, which
* includes the entry stack is excluded for everything.
+ *
+ * For FRED, nested #DB should just work fine. But when a watchpoint or
+ * breakpoint is set in the code path which is executed by #DB handler,
+ * it results in an endless recursion and stack overflow. Thus we stay
+ * with the IDT approach, i.e., save DR7 and disable #DB.
*/
unsigned long dr7 = local_db_save();
irqentry_state_t irq_state = irqentry_nmi_enter(regs);
@@ -977,7 +982,8 @@ static __always_inline void exc_debug_kernel(struct pt_regs *regs,
* Catch SYSENTER with TF set and clear DR_STEP. If this hit a
* watchpoint at the same time then that will still be handled.
*/
- if ((dr6 & DR_STEP) && is_sysenter_singlestep(regs))
+ if (!cpu_feature_enabled(X86_FEATURE_FRED) &&
+ (dr6 & DR_STEP) && is_sysenter_singlestep(regs))
dr6 &= ~DR_STEP;
/*
@@ -1009,8 +1015,7 @@ out:
local_db_restore(dr7);
}
-static __always_inline void exc_debug_user(struct pt_regs *regs,
- unsigned long dr6)
+static noinstr void exc_debug_user(struct pt_regs *regs, unsigned long dr6)
{
bool icebp;
@@ -1094,6 +1099,34 @@ DEFINE_IDTENTRY_DEBUG_USER(exc_debug)
{
exc_debug_user(regs, debug_read_clear_dr6());
}
+
+#ifdef CONFIG_X86_FRED
+/*
+ * When occurred on different ring level, i.e., from user or kernel
+ * context, #DB needs to be handled on different stack: User #DB on
+ * current task stack, while kernel #DB on a dedicated stack.
+ *
+ * This is exactly how FRED event delivery invokes an exception
+ * handler: ring 3 event on level 0 stack, i.e., current task stack;
+ * ring 0 event on the #DB dedicated stack specified in the
+ * IA32_FRED_STKLVLS MSR. So unlike IDT, the FRED debug exception
+ * entry stub doesn't do stack switch.
+ */
+DEFINE_FREDENTRY_DEBUG(exc_debug)
+{
+ /*
+ * FRED #DB stores DR6 on the stack in the format which
+ * debug_read_clear_dr6() returns for the IDT entry points.
+ */
+ unsigned long dr6 = fred_event_data(regs);
+
+ if (user_mode(regs))
+ exc_debug_user(regs, dr6);
+ else
+ exc_debug_kernel(regs, dr6);
+}
+#endif /* CONFIG_X86_FRED */
+
#else
/* 32 bit does not have separate entry points. */
DEFINE_IDTENTRY_RAW(exc_debug)
@@ -1369,8 +1402,34 @@ DEFINE_IDTENTRY_SW(iret_error)
}
#endif
+/* Do not enable FRED by default yet. */
+static bool enable_fred __ro_after_init = false;
+
+#ifdef CONFIG_X86_FRED
+static int __init fred_setup(char *str)
+{
+ if (!str)
+ return -EINVAL;
+
+ if (!cpu_feature_enabled(X86_FEATURE_FRED))
+ return 0;
+
+ if (!strcmp(str, "on"))
+ enable_fred = true;
+ else if (!strcmp(str, "off"))
+ enable_fred = false;
+ else
+ pr_warn("invalid FRED option: 'fred=%s'\n", str);
+ return 0;
+}
+early_param("fred", fred_setup);
+#endif
+
void __init trap_init(void)
{
+ if (cpu_feature_enabled(X86_FEATURE_FRED) && !enable_fred)
+ setup_clear_cpu_cap(X86_FEATURE_FRED);
+
/* Init cpu_entry_area before IST entries are set up */
setup_cpu_entry_areas();
@@ -1379,7 +1438,10 @@ void __init trap_init(void)
/* Initialize TSS before setting up traps so ISTs work */
cpu_init_exception_handling();
+
/* Setup traps as cpu_init() might #GP */
- idt_setup_traps();
+ if (!cpu_feature_enabled(X86_FEATURE_FRED))
+ idt_setup_traps();
+
cpu_init();
}