KVM: x86: Restore update of required xstate size in guest's CPUID
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Message ID 20200508233749.3417-1-sean.j.christopherson@intel.com
State New
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Series
  • KVM: x86: Restore update of required xstate size in guest's CPUID
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Commit Message

Sean Christopherson May 8, 2020, 11:37 p.m. UTC
Restore a guest CPUID update that was unintentional collateral damage
when the per-vCPU guest_xstate_size field was removed.

Cc: Xiaoyao Li <xiaoyao.li@intel.com>
Fixes: d87277414b851 ("kvm: x86: Cleanup vcpu->arch.guest_xstate_size")
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
---

There's nothing more thrilling than watching bisect home in on your own
commits, only to land on someone else's on the very last step.

 arch/x86/kvm/cpuid.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

Comments

Xiaoyao Li May 9, 2020, 2:09 a.m. UTC | #1
On 5/9/2020 7:37 AM, Sean Christopherson wrote:
> Restore a guest CPUID update that was unintentional collateral damage
> when the per-vCPU guest_xstate_size field was removed.

It's really unintentional. None of us noticed it. :(

It's good that you catch it!

> Cc: Xiaoyao Li <xiaoyao.li@intel.com>
> Fixes: d87277414b851 ("kvm: x86: Cleanup vcpu->arch.guest_xstate_size")
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> ---
> 
> There's nothing more thrilling than watching bisect home in on your own
> commits, only to land on someone else's on the very last step.
> 
>   arch/x86/kvm/cpuid.c | 6 ++++--
>   1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 35845704cf57a..cd708b0b460a0 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -84,11 +84,13 @@ int kvm_update_cpuid(struct kvm_vcpu *vcpu)
>   				   kvm_read_cr4_bits(vcpu, X86_CR4_PKE));
>   
>   	best = kvm_find_cpuid_entry(vcpu, 0xD, 0);
> -	if (!best)
> +	if (!best) {
>   		vcpu->arch.guest_supported_xcr0 = 0;
> -	else
> +	} else {
>   		vcpu->arch.guest_supported_xcr0 =
>   			(best->eax | ((u64)best->edx << 32)) & supported_xcr0;
> +		best->ebx = xstate_required_size(vcpu->arch.xcr0, false);
> +	}
>   
>   	best = kvm_find_cpuid_entry(vcpu, 0xD, 1);
>   	if (best && (cpuid_entry_has(best, X86_FEATURE_XSAVES) ||
>
Paolo Bonzini May 9, 2020, 12:51 p.m. UTC | #2
On 09/05/20 01:37, Sean Christopherson wrote:
> diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
> index 35845704cf57a..cd708b0b460a0 100644
> --- a/arch/x86/kvm/cpuid.c
> +++ b/arch/x86/kvm/cpuid.c
> @@ -84,11 +84,13 @@ int kvm_update_cpuid(struct kvm_vcpu *vcpu)
>  				   kvm_read_cr4_bits(vcpu, X86_CR4_PKE));
>  
>  	best = kvm_find_cpuid_entry(vcpu, 0xD, 0);
> -	if (!best)
> +	if (!best) {
>  		vcpu->arch.guest_supported_xcr0 = 0;
> -	else
> +	} else {
>  		vcpu->arch.guest_supported_xcr0 =
>  			(best->eax | ((u64)best->edx << 32)) & supported_xcr0;
> +		best->ebx = xstate_required_size(vcpu->arch.xcr0, false);
> +	}
>  
>  	best = kvm_find_cpuid_entry(vcpu, 0xD, 1);
>  	if (best && (cpuid_entry_has(best, X86_FEATURE_XSAVES) ||
> -- 2.26.0

Ugh, I'll write a testcase as penance.  Squashed, thanks.

Paolo

Patch
diff mbox series

diff --git a/arch/x86/kvm/cpuid.c b/arch/x86/kvm/cpuid.c
index 35845704cf57a..cd708b0b460a0 100644
--- a/arch/x86/kvm/cpuid.c
+++ b/arch/x86/kvm/cpuid.c
@@ -84,11 +84,13 @@  int kvm_update_cpuid(struct kvm_vcpu *vcpu)
 				   kvm_read_cr4_bits(vcpu, X86_CR4_PKE));
 
 	best = kvm_find_cpuid_entry(vcpu, 0xD, 0);
-	if (!best)
+	if (!best) {
 		vcpu->arch.guest_supported_xcr0 = 0;
-	else
+	} else {
 		vcpu->arch.guest_supported_xcr0 =
 			(best->eax | ((u64)best->edx << 32)) & supported_xcr0;
+		best->ebx = xstate_required_size(vcpu->arch.xcr0, false);
+	}
 
 	best = kvm_find_cpuid_entry(vcpu, 0xD, 1);
 	if (best && (cpuid_entry_has(best, X86_FEATURE_XSAVES) ||