[PATCH] KVM: TDX: Set SIGNIFCANT_INDEX flag for supported CPUIDs

[Changyuan Lyu]

Set the KVM_CPUID_FLAG_SIGNIFCANT_INDEX flag in the kvm_cpuid_entry2
structures returned by KVM_TDX_CAPABILITIES if the CPUID is indexed.
This ensures consistency with the CPUID entries returned by
KVM_GET_SUPPORTED_CPUID.

Additionally, add a WARN_ON_ONCE() to verify that the TDX module's
reported entries align with KVM's expectations regarding indexed
CPUID functions.

Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: Changyuan Lyu <changyuanl@xxxxxxxxxx>
---
 arch/x86/kvm/vmx/tdx.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index 2d7a4d52ccfb4..0c524f9a94a6c 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -172,9 +172,15 @@ static void td_init_cpuid_entry2(struct kvm_cpuid_entry2 *entry, unsigned char i
 	entry->ecx = (u32)td_conf->cpuid_config_values[idx][1];
 	entry->edx = td_conf->cpuid_config_values[idx][1] >> 32;
 
-	if (entry->index == KVM_TDX_CPUID_NO_SUBLEAF)
+	if (entry->index == KVM_TDX_CPUID_NO_SUBLEAF) {
 		entry->index = 0;
+		entry->flags &= ~KVM_CPUID_FLAG_SIGNIFCANT_INDEX;
+	} else {
+		entry->flags |= KVM_CPUID_FLAG_SIGNIFCANT_INDEX;
+	}
 
+	WARN_ON_ONCE(cpuid_function_is_indexed(entry->function) !=
+		     !!(entry->flags & KVM_CPUID_FLAG_SIGNIFCANT_INDEX));
 	/*
 	 * The TDX module doesn't allow configuring the guest phys addr bits
 	 * (EAX[23:16]).  However, KVM uses it as an interface to the userspace
-- 
2.53.0.371.g1d285c8824-goog