Just mark XFD as always supported for TDX. This simple solution relies
on the fact KVM will report XFD as 0 when it's not supported by the
hardware.

Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
---
 target/i386/cpu.h     | 1 +
 target/i386/kvm/tdx.c | 5 +++++
 2 files changed, 6 insertions(+)

diff --git a/target/i386/cpu.h b/target/i386/cpu.h
index 132312d70a54..a223e09a25c4 100644
--- a/target/i386/cpu.h
+++ b/target/i386/cpu.h
@@ -1126,6 +1126,7 @@ uint64_t x86_cpu_get_supported_feature_word(X86CPU *cpu, FeatureWord w);
 #define CPUID_XSAVE_XSAVEC     (1U << 1)
 #define CPUID_XSAVE_XGETBV1    (1U << 2)
 #define CPUID_XSAVE_XSAVES     (1U << 3)
+#define CPUID_XSAVE_XFD        (1U << 4)
 
 #define CPUID_6_EAX_ARAT       (1U << 2)
 
diff --git a/target/i386/kvm/tdx.c b/target/i386/kvm/tdx.c
index c7b4a098d12f..e07cd9a1ee15 100644
--- a/target/i386/kvm/tdx.c
+++ b/target/i386/kvm/tdx.c
@@ -620,6 +620,11 @@ static void tdx_add_supported_cpuid_by_xfam(void)
     e->edx |= (tdx_caps->supported_xfam & CPUID_XSTATE_XCR0_MASK) >> 32;
 
     e = find_in_supported_entry(0xd, 1);
+    /* Mark XFD always support for TDX, it will be cleared finally in
+     * tdx_adjust_cpuid_features() if XFD is unavailable on the hardware
+     * because in this case the original data has it as 0.
+     */
+    e->eax |= CPUID_XSAVE_XFD;
     e->ecx |= (tdx_caps->supported_xfam & CPUID_XSTATE_XSS_MASK);
     e->edx |= (tdx_caps->supported_xfam & CPUID_XSTATE_XSS_MASK) >> 32;
 }
-- 
2.34.1