Re: [PATCH] KVM: x86: Update the states size cpuid even if XCR0/IA32_XSS is reset

[Paolo Bonzini]

On 1/17/22 09:26, Like Xu wrote:
> From: Like Xu <likexu@xxxxxxxxxxx>
>
> XCR0 is reset to 1 by RESET but not INIT and IA32_XSS is zeroed by
> both RESET and INIT. In both cases, the size in bytes of the XSAVE
> area containing all states enabled by XCR0 or (XCRO | IA32_XSS)
> needs to be updated.
>
> Fixes: a554d207dc46 ("KVM: X86: Processor States following Reset or INIT")
> Signed-off-by: Like Xu <likexu@xxxxxxxxxxx>

Can you write a test case please?

Thanks,

Paolo

> ---
>   arch/x86/kvm/x86.c | 8 ++++++++
>   1 file changed, 8 insertions(+)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 76b4803dd3bd..5748a57e1cb7 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -11134,6 +11134,7 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>   	struct kvm_cpuid_entry2 *cpuid_0x1;
>   	unsigned long old_cr0 = kvm_read_cr0(vcpu);
>   	unsigned long new_cr0;
> +	bool need_update_cpuid = false;
>   
>   	/*
>   	 * Several of the "set" flows, e.g. ->set_cr0(), read other registers
> @@ -11199,6 +11200,8 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>   
>   		vcpu->arch.msr_misc_features_enables = 0;
>   
> +		if (vcpu->arch.xcr0 != XFEATURE_MASK_FP)
> +			need_update_cpuid = true;
>   		vcpu->arch.xcr0 = XFEATURE_MASK_FP;
>   	}
>   
> @@ -11216,6 +11219,8 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>   	cpuid_0x1 = kvm_find_cpuid_entry(vcpu, 1, 0);
>   	kvm_rdx_write(vcpu, cpuid_0x1 ? cpuid_0x1->eax : 0x600);
>   
> +	if (vcpu->arch.ia32_xss)
> +		need_update_cpuid = true;
>   	vcpu->arch.ia32_xss = 0;
>   
>   	static_call(kvm_x86_vcpu_reset)(vcpu, init_event);
> @@ -11264,6 +11269,9 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>   	 */
>   	if (init_event)
>   		kvm_make_request(KVM_REQ_TLB_FLUSH_GUEST, vcpu);
> +
> +	if (need_update_cpuid)
> +		kvm_update_cpuid_runtime(vcpu);
>   }
>   EXPORT_SYMBOL_GPL(kvm_vcpu_reset);
>