On Mon, Apr 15, 2013 at 11:30:13PM -0300, Marcelo Tosatti wrote:
>
> ** 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 <uobergfe@xxxxxxxxxx>
> Signed-off-by: Marcelo Tosatti <mtosatti@xxxxxxxxxx>
>
Reviewed-by: Gleb Natapov <gleb@xxxxxxxxxx>
> 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;
--
Gleb.
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