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

[Paolo Bonzini <pbonzini@redhat.com>]

From: Yan Zhao <yan.y.zhao@intel.com>

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@intel.com>
Message-ID: <20250224070832.31394-1-yan.y.zhao@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 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;
 		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