From: Eric Northup <digitaleric@xxxxxxxxxx>
Add a percpu boolean, tracking whether a KVM vCPU is running on the
host CPU. KVM will set and clear it as it loads/unloads guest XCR0.
(Note that the rest of the guest FPU load/restore is safe, because
kvm_load_guest_fpu and kvm_put_guest_fpu call __kernel_fpu_begin()
and __kernel_fpu_end(), respectively.) irq_fpu_usable() will then
also check for this percpu boolean.
---
arch/x86/include/asm/i387.h | 3 +++
arch/x86/kernel/i387.c | 10 ++++++++--
arch/x86/kvm/x86.c | 4 ++++
3 files changed, 15 insertions(+), 2 deletions(-)
diff --git a/arch/x86/include/asm/i387.h b/arch/x86/include/asm/i387.h
index ed8089d..ca2c173 100644
--- a/arch/x86/include/asm/i387.h
+++ b/arch/x86/include/asm/i387.h
@@ -14,6 +14,7 @@
#include <linux/sched.h>
#include <linux/hardirq.h>
+#include <linux/percpu.h>
struct pt_regs;
struct user_i387_struct;
@@ -25,6 +26,8 @@ extern void math_state_restore(void);
extern bool irq_fpu_usable(void);
+DECLARE_PER_CPU(bool, kvm_xcr0_loaded);
+
/*
* Careful: __kernel_fpu_begin/end() must be called with preempt disabled
* and they don't touch the preempt state on their own.
diff --git a/arch/x86/kernel/i387.c b/arch/x86/kernel/i387.c
index b627746..9015828 100644
--- a/arch/x86/kernel/i387.c
+++ b/arch/x86/kernel/i387.c
@@ -19,6 +19,9 @@
#include <asm/fpu-internal.h>
#include <asm/user.h>
+DEFINE_PER_CPU(bool, kvm_xcr0_loaded);
+EXPORT_PER_CPU_SYMBOL(kvm_xcr0_loaded);
+
/*
* Were we in an interrupt that interrupted kernel mode?
*
@@ -33,8 +36,11 @@
*/
static inline bool interrupted_kernel_fpu_idle(void)
{
- if (use_eager_fpu())
- return __thread_has_fpu(current);
+ if (use_eager_fpu()) {
+ /* Preempt already disabled, safe to read percpu. */
+ return __thread_has_fpu(current) &&
+ !__this_cpu_read(kvm_xcr0_loaded);
+ }
return !__thread_has_fpu(current) &&
(read_cr0() & X86_CR0_TS);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index d21bce5..f0ba7a1 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -557,8 +557,10 @@ EXPORT_SYMBOL_GPL(kvm_lmsw);
static void kvm_load_guest_xcr0(struct kvm_vcpu *vcpu)
{
+ BUG_ON(this_cpu_read(kvm_xcr0_loaded) != vcpu->guest_xcr0_loaded);
if (kvm_read_cr4_bits(vcpu, X86_CR4_OSXSAVE) &&
!vcpu->guest_xcr0_loaded) {
+ this_cpu_write(kvm_xcr0_loaded, 1);
/* kvm_set_xcr() also depends on this */
xsetbv(XCR_XFEATURE_ENABLED_MASK, vcpu->arch.xcr0);
vcpu->guest_xcr0_loaded = 1;
@@ -571,7 +573,9 @@ static void kvm_put_guest_xcr0(struct kvm_vcpu *vcpu)
if (vcpu->arch.xcr0 != host_xcr0)
xsetbv(XCR_XFEATURE_ENABLED_MASK, host_xcr0);
vcpu->guest_xcr0_loaded = 0;
+ this_cpu_write(kvm_xcr0_loaded, 0);
}
+ BUG_ON(this_cpu_read(kvm_xcr0_loaded) != vcpu->guest_xcr0_loaded);
}
int __kvm_set_xcr(struct kvm_vcpu *vcpu, u32 index, u64 xcr)
--
2.7.0.rc3.207.g0ac5344
--
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