From: Jan Beulich <jbeulich@xxxxxxxxxx>
Touching of the floating point state in a kernel debugger must be
NMI-safe, specifically math_state_restore() must be able to deal with
being called out of an NMI context. In order to do that reliably, the
context switch code must take care to not leave a window open where
the current task's TS_USEDFPU flag and CR0.TS could get out of sync.
Signed-Off-By: Jan Beulich <jbeulich@xxxxxxxxxx>
Signed-off-by: Andi Kleen <ak@xxxxxxx>
arch/x86_64/kernel/pmtimer.c | 3 ++-
arch/x86_64/kernel/process.c | 17 ++++++++++++++---
2 files changed, 16 insertions(+), 4 deletions(-)
Index: linux/arch/x86_64/kernel/process.c
===================================================================
--- linux.orig/arch/x86_64/kernel/process.c
+++ linux/arch/x86_64/kernel/process.c
@@ -527,8 +527,6 @@ __switch_to(struct task_struct *prev_p,
int cpu = smp_processor_id();
struct tss_struct *tss = &per_cpu(init_tss, cpu);
- unlazy_fpu(prev_p);
-
/*
* Reload esp0, LDT and the page table pointer:
*/
@@ -586,11 +584,14 @@ __switch_to(struct task_struct *prev_p,
}
/*
- * Switch the PDA context.
+ * Switch the PDA and FPU contexts.
*/
prev->userrsp = read_pda(oldrsp);
write_pda(oldrsp, next->userrsp);
write_pda(pcurrent, next_p);
+ /* This must be here to ensure both math_state_restore() and
+ kernel_fpu_begin() work consistently. */
+ unlazy_fpu(prev_p);
write_pda(kernelstack,
task_stack_page(next_p) + THREAD_SIZE - PDA_STACKOFFSET);
@@ -841,3 +842,13 @@ unsigned long arch_align_stack(unsigned
sp -= get_random_int() % 8192;
return sp & ~0xf;
}
+
+unsigned long last_clier;
+
+void local_irq_disable(void)
+{
+ if (!irqs_disabled()) {
+ last_clier = __builtin_return_address(0);
+ asm volatile("cli":::"memory");
+ }
+}
Index: linux/arch/x86_64/kernel/pmtimer.c
===================================================================
--- linux.orig/arch/x86_64/kernel/pmtimer.c
+++ linux/arch/x86_64/kernel/pmtimer.c
@@ -86,7 +86,7 @@ static unsigned pmtimer_wait_tick(void)
for (a = b = inl(pmtmr_ioport) & ACPI_PM_MASK;
a == b;
b = inl(pmtmr_ioport) & ACPI_PM_MASK)
- ;
+ cpu_relax();
return b;
}
@@ -97,6 +97,7 @@ void pmtimer_wait(unsigned us)
a = pmtimer_wait_tick();
do {
b = inl(pmtmr_ioport);
+ cpu_relax();
} while (cyc2us(b - a) < us);
}
-
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