Re: [PATCH v2 08/11] KVM: x86: Add is_vm_type_supported callback

[Sean Christopherson]

On Fri, Feb 23, 2024, Paolo Bonzini wrote:
> Allow the backend to specify which VM types are supported.

Hmm, rather than another kvm_x86_ops hook, I vote to add kvm_caps.supported_vm_types,
and use the existing harware_setup() hook to fill in the vendor specific types.

As a very incomplete stub:

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 3bc69b0c9822..bb7d979db2df 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4576,17 +4576,9 @@ static int kvm_ioctl_get_supported_hv_cpuid(struct kvm_vcpu *vcpu,
 }
 #endif
 
-static inline bool __kvm_is_vm_type_supported(unsigned long type)
-{
-       return type == KVM_X86_DEFAULT_VM ||
-              (type == KVM_X86_SW_PROTECTED_VM &&
-               IS_ENABLED(CONFIG_KVM_SW_PROTECTED_VM) && tdp_mmu_enabled);
-}
-
 static bool kvm_is_vm_type_supported(unsigned long type)
 {
-       return __kvm_is_vm_type_supported(type) ||
-              static_call(kvm_x86_is_vm_type_supported)(type);
+       return kvm_caps.supported_vm_types & BIT(type);
 }
 
 int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
@@ -4787,13 +4779,7 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
                r = kvm_caps.has_notify_vmexit;
                break;
        case KVM_CAP_VM_TYPES:
-               r = BIT(KVM_X86_DEFAULT_VM);
-               if (kvm_is_vm_type_supported(KVM_X86_SW_PROTECTED_VM))
-                       r |= BIT(KVM_X86_SW_PROTECTED_VM);
-               if (kvm_is_vm_type_supported(KVM_X86_SEV_VM))
-                       r |= BIT(KVM_X86_SEV_VM);
-               if (kvm_is_vm_type_supported(KVM_X86_SEV_ES_VM))
-                       r |= BIT(KVM_X86_SEV_ES_VM);
+               r = kvm_caps.supported_vm_types;
                break;
        default:
                break;
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index 2f7e19166658..802ac1ead055 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -29,6 +29,8 @@ struct kvm_caps {
        u64 supported_xcr0;
        u64 supported_xss;
        u64 supported_perf_cap;
+
+       u32 supported_vm_types;
 };
 
 void kvm_spurious_fault(void);