Since commit c6bd2dd63420 ("i386/cpu: Set up CPUID_HT in
x86_cpu_expand_features() instead of cpu_x86_cpuid()") and
commit 99a637a86f55 ("i386/cpu: Set and track CPUID_EXT3_CMP_LEG in
env->features[FEAT_8000_0001_ECX]"), it gets warnings when booting the
VM with vcpus >= 2 and with tcg:

  qemu-system-x86_64: warning: TCG doesn't support requested feature: CPUID.01H:EDX.ht [bit 28]
  qemu-system-x86_64: warning: TCG doesn't support requested feature: CPUID.80000001H:ECX.cmp-legacy [bit 1]

This is because, after the two commits, CPUID_HT and CPUID_EXT3_CMP_LEG
are set in env->features[] when vcpus >=2 (in x86_cpu_expand_features())
later in x86_cpu_filter_features() it will check against the TCG supported
bits. However, current TCG doesn't mark the two bits as supported, hence
the warnings.

Fix it by adding the two bits to the supported bits of TCG since multiple
vcpus are supported by TCG.

Fixes: c6bd2dd63420 ("i386/cpu: Set up CPUID_HT in x86_cpu_expand_features() instead of cpu_x86_cpuid()")
Fixes: 99a637a86f55 ("i386/cpu: Set and track CPUID_EXT3_CMP_LEG in env->features[FEAT_8000_0001_ECX]")
Reported-by: Ewan Hai <ewanhai-oc@zhaoxin.com>
Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
---
 target/i386/cpu.c | 8 +++++---
 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index 1ca6307c72ef..c5a1fe1e8afe 100644
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -776,11 +776,12 @@ void x86_cpu_vendor_words2str(char *dst, uint32_t vendor1,
           CPUID_PAE | CPUID_MCE | CPUID_CX8 | CPUID_APIC | CPUID_SEP | \
           CPUID_MTRR | CPUID_PGE | CPUID_MCA | CPUID_CMOV | CPUID_PAT | \
           CPUID_PSE36 | CPUID_CLFLUSH | CPUID_ACPI | CPUID_MMX | \
-          CPUID_FXSR | CPUID_SSE | CPUID_SSE2 | CPUID_SS | CPUID_DE)
+          CPUID_FXSR | CPUID_SSE | CPUID_SSE2 | CPUID_SS | CPUID_DE | \
+          CPUID_HT)
           /* partly implemented:
           CPUID_MTRR, CPUID_MCA, CPUID_CLFLUSH (needed for Win64) */
           /* missing:
-          CPUID_VME, CPUID_DTS, CPUID_SS, CPUID_HT, CPUID_TM, CPUID_PBE */
+          CPUID_VME, CPUID_DTS, CPUID_SS, CPUID_TM, CPUID_PBE */
 
 /*
  * Kernel-only features that can be shown to usermode programs even if
@@ -848,7 +849,8 @@ void x86_cpu_vendor_words2str(char *dst, uint32_t vendor1,
 
 #define TCG_EXT3_FEATURES (CPUID_EXT3_LAHF_LM | CPUID_EXT3_SVM | \
           CPUID_EXT3_CR8LEG | CPUID_EXT3_ABM | CPUID_EXT3_SSE4A | \
-          CPUID_EXT3_3DNOWPREFETCH | CPUID_EXT3_KERNEL_FEATURES)
+          CPUID_EXT3_3DNOWPREFETCH | CPUID_EXT3_KERNEL_FEATURES | \
+          CPUID_EXT3_CMP_LEG)
 
 #define TCG_EXT4_FEATURES 0
 
-- 
2.43.0

On Tue, May 13, 2025 at 11:16:51PM -0400, Xiaoyao Li wrote:
> Date: Tue, 13 May 2025 23:16:51 -0400
> From: Xiaoyao Li <xiaoyao.li@intel.com>
> Subject: [PATCH 1/2] i386/tcg: Make CPUID_HT and CPUID_EXT3_CMP_LEG
>  supported
> X-Mailer: git-send-email 2.43.0
> 
> Since commit c6bd2dd63420 ("i386/cpu: Set up CPUID_HT in
> x86_cpu_expand_features() instead of cpu_x86_cpuid()") and
> commit 99a637a86f55 ("i386/cpu: Set and track CPUID_EXT3_CMP_LEG in
> env->features[FEAT_8000_0001_ECX]"), it gets warnings when booting the
> VM with vcpus >= 2 and with tcg:
> 
>   qemu-system-x86_64: warning: TCG doesn't support requested feature: CPUID.01H:EDX.ht [bit 28]
>   qemu-system-x86_64: warning: TCG doesn't support requested feature: CPUID.80000001H:ECX.cmp-legacy [bit 1]
> 
> This is because, after the two commits, CPUID_HT and CPUID_EXT3_CMP_LEG
> are set in env->features[] when vcpus >=2 (in x86_cpu_expand_features())
> later in x86_cpu_filter_features() it will check against the TCG supported
> bits. However, current TCG doesn't mark the two bits as supported, hence
> the warnings.
> 
> Fix it by adding the two bits to the supported bits of TCG since multiple
> vcpus are supported by TCG.
> 
> Fixes: c6bd2dd63420 ("i386/cpu: Set up CPUID_HT in x86_cpu_expand_features() instead of cpu_x86_cpuid()")
> Fixes: 99a637a86f55 ("i386/cpu: Set and track CPUID_EXT3_CMP_LEG in env->features[FEAT_8000_0001_ECX]")
> Reported-by: Ewan Hai <ewanhai-oc@zhaoxin.com>

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/2894

Then QEMU gitlab can track this fix.

> Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
> ---
>  target/i386/cpu.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)

Both HT and CMPLegacy depend on CPU topology (mutiple threads per
package), therefore, there's no need for extra work in TCG.

So,

Reviewed-by: Zhao Liu <zhao1.liu@intel.com>