Re: [PATCH 2/4] KVM: x86: Introduce supported_quirks to block disabling quirks

[Xiaoyao Li <xiaoyao.li@xxxxxxxxx>]

On 3/1/2025 3:34 PM, Paolo Bonzini wrote:
> From: Yan Zhao <yan.y.zhao@xxxxxxxxx>
>
> Introduce supported_quirks in kvm_caps to store platform-specific force-enabled
> quirks.  Any quirk removed from kvm_caps.supported_quirks will never be
> included in kvm->arch.disabled_quirks, and will cause the ioctl to fail if
> passed to KVM_ENABLE_CAP(KVM_CAP_DISABLE_QUIRKS2).
>
> Signed-off-by: Yan Zhao <yan.y.zhao@xxxxxxxxx>
> Message-ID: <20250224070832.31394-1-yan.y.zhao@xxxxxxxxx>
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> ---
>   arch/x86/kvm/x86.c | 7 ++++---
>   arch/x86/kvm/x86.h | 2 ++
>   2 files changed, 6 insertions(+), 3 deletions(-)
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index fd0a44e59314..a97e58916b6a 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -4782,7 +4782,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>   		r = enable_pmu ? KVM_CAP_PMU_VALID_MASK : 0;
>   		break;
>   	case KVM_CAP_DISABLE_QUIRKS2:
> -		r = KVM_X86_VALID_QUIRKS;
> +		r = kvm_caps.supported_quirks;
>   		break;
>   	case KVM_CAP_X86_NOTIFY_VMEXIT:
>   		r = kvm_caps.has_notify_vmexit;
> @@ -6521,11 +6521,11 @@ int kvm_vm_ioctl_enable_cap(struct kvm *kvm,
>   	switch (cap->cap) {
>   	case KVM_CAP_DISABLE_QUIRKS2:
>   		r = -EINVAL;
> -		if (cap->args[0] & ~KVM_X86_VALID_QUIRKS)
> +		if (cap->args[0] & ~kvm_caps.supported_quirks)
>   			break;
>   		fallthrough;
>   	case KVM_CAP_DISABLE_QUIRKS:
> -		kvm->arch.disabled_quirks = cap->args[0];
> +		kvm->arch.disabled_quirks = cap->args[0] & kvm_caps.supported_quirks;

Don't need this. It's redundant with the above, which ensures
cap->args[0] is the subset of kvm_caps.supported_quirks

Otherwise,

Reviewed-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>

>   		r = 0;
>   		break;
>   	case KVM_CAP_SPLIT_IRQCHIP: {
> @@ -9775,6 +9775,7 @@ int kvm_x86_vendor_init(struct kvm_x86_init_ops *ops)
>   		kvm_host.xcr0 = xgetbv(XCR_XFEATURE_ENABLED_MASK);
>   		kvm_caps.supported_xcr0 = kvm_host.xcr0 & KVM_SUPPORTED_XCR0;
>   	}
> +	kvm_caps.supported_quirks = KVM_X86_VALID_QUIRKS;
>   	kvm_caps.inapplicable_quirks = 0;
>   
>   	rdmsrl_safe(MSR_EFER, &kvm_host.efer);
> diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
> index 9af199c8e5c8..f2672b14388c 100644
> --- a/arch/x86/kvm/x86.h
> +++ b/arch/x86/kvm/x86.h
> @@ -34,6 +34,8 @@ struct kvm_caps {
>   	u64 supported_xcr0;
>   	u64 supported_xss;
>   	u64 supported_perf_cap;
> +
> +	u64 supported_quirks;
>   	u64 inapplicable_quirks;
>   };
>