On Sat, Mar 01, 2025 at 02:34:25AM -0500, Paolo Bonzini wrote:
> In some cases, the handling of quirks is split between platform-specific
> code and generic code, or it is done entirely in generic code, but the
> relevant bug does not trigger on some platforms; for example,
> KVM_X86_QUIRK_CD_NW_CLEARED is only applicable to AMD systems. In that
> case, allow unaffected vendor modules to disable handling of the quirk.
>
> The quirk remains available in KVM_CAP_DISABLE_QUIRKS2, because that API
> tells userspace that KVM *knows* that some of its past behavior was bogus
> or just undesirable. In other words, it's plausible for userspace to
> refuse to run if a quirk is not listed by KVM_CAP_DISABLE_QUIRKS2.
>
> In kvm_check_has_quirk(), in addition to checking if a quirk is not
> explicitly disabled by the user, also verify if the quirk applies to
> the hardware.
>
> 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/vmx/vmx.c | 1 +
> arch/x86/kvm/x86.c | 1 +
> arch/x86/kvm/x86.h | 12 +++++++-----
> 3 files changed, 9 insertions(+), 5 deletions(-)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 486fbdb4365c..75df4caea2f7 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -8506,6 +8506,7 @@ __init int vmx_hardware_setup(void)
>
> kvm_set_posted_intr_wakeup_handler(pi_wakeup_handler);
>
> + kvm_caps.inapplicable_quirks = KVM_X86_QUIRK_CD_NW_CLEARED;
As you mentioned, KVM_X86_QUIRK_CD_NW_CLEARED has no effect on Intel's
platforms, no matter kvm_check_has_quirk() returns true or false.
So, what's the purpose to introduce kvm_caps.inapplicable_quirks?
One concern is that since KVM_X86_QUIRK_CD_NW_CLEARED is not for Intel
platforms, it's unnatural for Intel's code to add it into the
kvm_caps.inapplicable_quirks.
If AMD introduces new quirks that apply only to its own platform in future,
they may have no idea whether it's applicable to Intel as well.
> return r;
> }
>
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 856ceeb4fb35..fd0a44e59314 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -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.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 8ce6da98b5a2..9af199c8e5c8 100644
> --- a/arch/x86/kvm/x86.h
> +++ b/arch/x86/kvm/x86.h
> @@ -34,6 +34,7 @@ struct kvm_caps {
> u64 supported_xcr0;
> u64 supported_xss;
> u64 supported_perf_cap;
> + u64 inapplicable_quirks;
> };
>
> struct kvm_host_values {
> @@ -354,11 +355,6 @@ static inline void kvm_register_write(struct kvm_vcpu *vcpu,
> return kvm_register_write_raw(vcpu, reg, val);
> }
>
> -static inline bool kvm_check_has_quirk(struct kvm *kvm, u64 quirk)
> -{
> - return !(kvm->arch.disabled_quirks & quirk);
> -}
> -
> void kvm_inject_realmode_interrupt(struct kvm_vcpu *vcpu, int irq, int inc_eip);
>
> u64 get_kvmclock_ns(struct kvm *kvm);
> @@ -394,6 +390,12 @@ extern struct kvm_host_values kvm_host;
>
> extern bool enable_pmu;
>
> +static inline bool kvm_check_has_quirk(struct kvm *kvm, u64 quirk)
> +{
> + u64 disabled_quirks = kvm_caps.inapplicable_quirks | kvm->arch.disabled_quirks;
> + return !(disabled_quirks & quirk);
> +}
> +
> /*
> * Get a filtered version of KVM's supported XCR0 that strips out dynamic
> * features for which the current process doesn't (yet) have permission to use.
> --
> 2.43.5
>
>
