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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 3/3/25 02:23, Yan Zhao wrote: > On Sat, Mar 01, 2025 at 02:34:26AM -0500, Paolo Bonzini wrote: >> From: Yan Zhao >> >> 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 >> Message-ID: <20250224070832.31394-1-yan.y.zhao@intel.com> >> Signed-off-by: Paolo Bonzini >> --- >> 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; > > As the concern raised in [1], it's confusing for > KVM_X86_QUIRK_EPT_IGNORE_GUEST_PAT to be present on AMD's platforms while not > present on Intel's non-self-snoop platforms. To make it less confusing, let's rename it to KVM_X86_QUIRK_IGNORE_GUEST_PAT. So if userspace wants to say "I don't want KVM to ignore guest's PAT!", it can do so easily: - it can check unconditionally that the quirk is included in KVM_CAP_DISABLE_QUIRKS2, and it will pass on both Intel with self-snoop with AMD; - it can pass it unconditionally to KVM_X86_QUIRK_IGNORE_GUEST_PAT, knowing that PAT will be honored. But KVM_CHECK_EXTENSION(KVM_CAP_DISABLE_QUIRKS2) will *not* include the quirk on Intel without self-snoop, which lets userspace detect the condition and raise an error. This is better than introducing a new case in the API "the bit is returned by KVM_CHECK_EXTENSION, but rejected by KVM_ENABLE_CAP". Such a new case would inevitably lead to KVM_CAP_DISABLE_QUIRKS3. :) > Or what about introduce kvm_caps.force_enabled_quirk? > > if (!static_cpu_has(X86_FEATURE_SELFSNOOP)) > kvm_caps.force_enabled_quirks |= KVM_X86_QUIRK_EPT_IGNORE_GUEST_PAT; That would also make it harder for userspace to understand what's going on. > [1] https://lore.kernel.org/all/Z8UBpC76CyxCIRiU@yzhao56-desk.sh.intel.com/ >> 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; > > Will this break the uapi of KVM_CAP_DISABLE_QUIRKS? > My understanding is that only KVM_CAP_DISABLE_QUIRKS2 filters out invalid > quirks. The difference between KVM_CAP_DISABLE_QUIRKS and KVM_CAP_DISABLE_QUIRKS2 is only that invalid values do not cause an error; but userspace cannot know what is in kvm->arch.disabled_quirks, so KVM can change the value that is stored there. Paolo >> 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; >> }; >> >> -- >> 2.43.5 >> >> >