** Untested **.
Emulation of xcr0 writes zero guest_xcr0_loaded variable so that
subsequent VM-entry reloads CPU's xcr0 with guests xcr0 value.
However, this is incorrect because guest_xcr0_loaded variable is
read to decide whether to reload hosts xcr0.
In case the vcpu thread is scheduled out after the guest_xcr0_loaded = 0
assignment, and scheduler decides to preload FPU:
switch_to
{
__switch_to
__math_state_restore
restore_fpu_checking
fpu_restore_checking
if (use_xsave())
fpu_xrstor_checking
xrstor64 with CPU's xcr0 == guests xcr0
Fix by properly restoring hosts xcr0 during emulation of xcr0 writes.
Analyzed-by: Ulrich Obergfell <uober...@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosa...@redhat.com>
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 999d124..222926a 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -555,6 +555,25 @@ void kvm_lmsw(struct kvm_vcpu *vcpu, unsigned long msw)
}
EXPORT_SYMBOL_GPL(kvm_lmsw);
+static void kvm_load_guest_xcr0(struct kvm_vcpu *vcpu)
+{
+ if (kvm_read_cr4_bits(vcpu, X86_CR4_OSXSAVE) &&
+ !vcpu->guest_xcr0_loaded) {
+ /* kvm_set_xcr() also depends on this */
+ xsetbv(XCR_XFEATURE_ENABLED_MASK, vcpu->arch.xcr0);
+ vcpu->guest_xcr0_loaded = 1;
+ }
+}
+
+static void kvm_put_guest_xcr0(struct kvm_vcpu *vcpu)
+{
+ if (vcpu->guest_xcr0_loaded) {
+ if (vcpu->arch.xcr0 != host_xcr0)
+ xsetbv(XCR_XFEATURE_ENABLED_MASK, host_xcr0);
+ vcpu->guest_xcr0_loaded = 0;
+ }
+}
+
int __kvm_set_xcr(struct kvm_vcpu *vcpu, u32 index, u64 xcr)
{
u64 xcr0;
@@ -571,8 +590,8 @@ int __kvm_set_xcr(struct kvm_vcpu *vcpu, u32 index, u64 xcr)
return 1;
if (xcr0 & ~host_xcr0)
return 1;
+ kvm_put_guest_xcr0(vcpu);
vcpu->arch.xcr0 = xcr0;
- vcpu->guest_xcr0_loaded = 0;
return 0;
}
@@ -5600,25 +5619,6 @@ static void inject_pending_event(struct kvm_vcpu *vcpu)
}
}
-static void kvm_load_guest_xcr0(struct kvm_vcpu *vcpu)
-{
- if (kvm_read_cr4_bits(vcpu, X86_CR4_OSXSAVE) &&
- !vcpu->guest_xcr0_loaded) {
- /* kvm_set_xcr() also depends on this */
- xsetbv(XCR_XFEATURE_ENABLED_MASK, vcpu->arch.xcr0);
- vcpu->guest_xcr0_loaded = 1;
- }
-}
-
-static void kvm_put_guest_xcr0(struct kvm_vcpu *vcpu)
-{
- if (vcpu->guest_xcr0_loaded) {
- if (vcpu->arch.xcr0 != host_xcr0)
- xsetbv(XCR_XFEATURE_ENABLED_MASK, host_xcr0);
- vcpu->guest_xcr0_loaded = 0;
- }
-}
-
static void process_nmi(struct kvm_vcpu *vcpu)
{
unsigned limit = 2;
--
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