KVM: x86: Introduce supported_quirks to block disabling quirks

JIRA: https://issues.redhat.com/browse/RHEL-47242

commit bd7d536
Author: Yan Zhao <yan.y.zhao@intel.com>
Date:   Mon Feb 24 15:08:32 2025 +0800

    KVM: x86: Introduce supported_quirks to block disabling quirks

    Introduce supported_quirks in kvm_caps to store platform-specific force-enabled
    quirks.

    No functional changes intended.

    Signed-off-by: Yan Zhao <yan.y.zhao@intel.com>
    Message-ID: <20250224070832.31394-1-yan.y.zhao@intel.com>
    [Remove unsupported quirks at KVM_ENABLE_CAP time. - Paolo]
    Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>

Author: Maxim Levitsky

arch/x86/kvm/x86.c

@@ -4807,7 +4807,7 @@ 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;
@@ -6546,11 +6546,11 @@ 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: {
@@ -9792,6 +9792,7 @@ 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 = KVM_X86_CONDITIONAL_QUIRKS;
 
 	rdmsrl_safe(MSR_EFER, &kvm_host.efer);
@@ -12748,7 +12749,7 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
 	/* Decided by the vendor code for other VM types.  */
 	kvm->arch.pre_fault_allowed =
 		type == KVM_X86_DEFAULT_VM || type == KVM_X86_SW_PROTECTED_VM;
-	kvm->arch.disabled_quirks = kvm_caps.inapplicable_quirks;
+	kvm->arch.disabled_quirks = kvm_caps.inapplicable_quirks & kvm_caps.supported_quirks;
 
 	ret = kvm_page_track_init(kvm);
 	if (ret)

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;
 };