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Subject[PATCH 1/2] KVM: x86: fix KVM_SET_XCRS for CPUs that do not support XSAVE
Date
The KVM_SET_XCRS ioctl must accept anything that KVM_GET_XCRS
could return. XCR0's bit 0 is always 1 in real processors with
XSAVE, and KVM_GET_XCRS will always leave bit 0 set even if the
emulated processor does not have XSAVE. So, KVM_SET_XCRS must
ignore that bit when checking for attempts to enable unsupported
save states.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
Introduced between v2 and v3, when I stopped hardcoding
XSTATE_FPSSE in guest_supported_xcr0.

arch/x86/kvm/x86.c | 11 ++++++++++-
1 file changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c951c71..f4e1391 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -577,6 +577,7 @@ static void kvm_put_guest_xcr0(struct kvm_vcpu *vcpu)
int __kvm_set_xcr(struct kvm_vcpu *vcpu, u32 index, u64 xcr)
{
u64 xcr0;
+ u64 valid_bits;

/* Only support XCR_XFEATURE_ENABLED_MASK(xcr0) now */
if (index != XCR_XFEATURE_ENABLED_MASK)
@@ -586,8 +587,16 @@ int __kvm_set_xcr(struct kvm_vcpu *vcpu, u32 index, u64 xcr)
return 1;
if ((xcr0 & XSTATE_YMM) && !(xcr0 & XSTATE_SSE))
return 1;
- if (xcr0 & ~vcpu->arch.guest_supported_xcr0)
+
+ /*
+ * Do not allow the guest to set bits that we do not support
+ * saving. However, xcr0 bit 0 is always set, even if the
+ * emulated CPU does not support XSAVE (see fx_init).
+ */
+ valid_bits = vcpu->arch.guest_supported_xcr0 | XSTATE_FP;
+ if (xcr0 & ~valid_bits)
return 1;
+
kvm_put_guest_xcr0(vcpu);
vcpu->arch.xcr0 = xcr0;
return 0;
--
1.8.3.1



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