Commit 42bdf991 authored by Marcelo Tosatti's avatar Marcelo Tosatti Committed by Gleb Natapov
Browse files

KVM: x86: fix maintenance of guest/host xcr0 state 



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: default avatarUlrich Obergfell <uobergfe@redhat.com>
Signed-off-by: default avatarMarcelo Tosatti <mtosatti@redhat.com>
Reviewed-by: default avatarPaolo Bonzini <pbonzini@redhat.com>
Signed-off-by: default avatarGleb Natapov <gleb@redhat.com>
parent 5af43c24

arch/x86/kvm/x86.c

+20 −20
Original line number Diff line number Diff line
@@ -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;

}
@@ -5614,25 +5633,6 @@ 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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