[PATCH 2/4] KVM: TDX: Set SIGNIFCANT_INDEX flag as appropriate when filling CPUID entries

[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,
otherwise KVM could confuse userspace and induce a configuration error.
This also ensures consistency with the CPUID entries returned by
KVM_GET_SUPPORTED_CPUID.

Fixes: 61bb28279623 ("KVM: TDX: Get system-wide info about TDX module on initialization")
Cc: stable@xxxxxxxxxxxxxxx
Suggested-by: Sean Christopherson <seanjc@xxxxxxxxxx>
Signed-off-by: Changyuan Lyu <changyuanl@xxxxxxxxxx>
[sean: keep the WARN, don't key off KVM_TDX_CPUID_NO_SUBLEAF]
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
 arch/x86/kvm/vmx/tdx.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c
index ee1d412b0ee6..bcfecd2b1f31 100644
--- a/arch/x86/kvm/vmx/tdx.c
+++ b/arch/x86/kvm/vmx/tdx.c
@@ -2,6 +2,7 @@
 #include <linux/cleanup.h>
 #include <linux/cpu.h>
 #include <asm/cpufeature.h>
+#include <asm/cpuid/api.h>
 #include <asm/fpu/xcr.h>
 #include <linux/misc_cgroup.h>
 #include <linux/mmu_context.h>
@@ -163,11 +164,18 @@ static void td_init_cpuid_entry2(struct kvm_cpuid_entry2 *entry, unsigned char i
 
 	entry->function = (u32)td_conf->cpuid_config_leaves[idx];
 	entry->index = td_conf->cpuid_config_leaves[idx] >> 32;
+	entry->flags = 0;
 	entry->eax = (u32)td_conf->cpuid_config_values[idx][0];
 	entry->ebx = td_conf->cpuid_config_values[idx][0] >> 32;
 	entry->ecx = (u32)td_conf->cpuid_config_values[idx][1];
 	entry->edx = td_conf->cpuid_config_values[idx][1] >> 32;
 
+	if (cpuid_function_is_indexed(entry->function))
+		entry->flags |= KVM_CPUID_FLAG_SIGNIFCANT_INDEX;
+
+	WARN_ON_ONCE(cpuid_function_is_indexed(entry->function) !=
+		     (entry->index != KVM_TDX_CPUID_NO_SUBLEAF));
+
 	if (entry->index == KVM_TDX_CPUID_NO_SUBLEAF)
 		entry->index = 0;
 
-- 
2.56.0.176.g3575e65682-goog


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