i386/cpu: Reorganize dependency check for arch lbr state

The arch lbr state has 2 dependencies:
 * Arch lbr feature bit (CPUID 0x7.0x0:EDX[bit 19]):

   This bit also depends on pmu property. Mask it off if pmu is disabled
   in x86_cpu_expand_features(), so that it is not needed to repeatedly
   check whether this bit is set as well as pmu is enabled.

   Note this doesn't need compat option, since even KVM hasn't support
   arch lbr yet.

   The supported xstate is constructed based such dependency in
   cpuid_has_xsave_feature(), so if pmu is disabled and arch lbr bit is
   masked off, then arch lbr state won't be included in supported
   xstates.

   Thus it's safe to drop the check on arch lbr bit in CPUID 0xD
   encoding.

 * XSAVES feature bit (CPUID 0xD.0x1.EAX[bit 3]):

   Arch lbr state is a supervisor state, which requires the XSAVES
   feature support. Enumerate supported supervisor state based on XSAVES
   feature bit in x86_cpu_enable_xsave_components().

   Then it's safe to drop the check on XSAVES feature support during
   CPUID 0XD encoding.

Suggested-by: Zide Chen <zide.chen@intel.com>
Tested-by: Farrah Chen <farrah.chen@intel.com>
Reviewed-by: Zide Chen <zide.chen@intel.com>
Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
Link: https://lore.kernel.org/r/20251211060801.3600039-8-zhao1.liu@intel.com
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/target/i386/cpu.c b/target/i386/cpu.c
index f4c0ae533d088f5864894cf4527a1f7df584a65a..b53467eb997bb8a9aa489b32cd08e2b0178e5a2d 100644 (file)
--- a/target/i386/cpu.c
+++ b/target/i386/cpu.c
@@ -8179,20 +8179,6 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
             *ebx = xsave_area_size(xstate, true);
             *ecx = env->features[FEAT_XSAVE_XSS_LO];
             *edx = env->features[FEAT_XSAVE_XSS_HI];
-            if (kvm_enabled() && cpu->enable_pmu &&
-                (env->features[FEAT_7_0_EDX] & CPUID_7_0_EDX_ARCH_LBR) &&
-                (*eax & CPUID_XSAVE_XSAVES)) {
-                *ecx |= XSTATE_ARCH_LBR_MASK;
-            } else {
-                *ecx &= ~XSTATE_ARCH_LBR_MASK;
-            }
-        } else if (count == 0xf && cpu->enable_pmu
-                   && (env->features[FEAT_7_0_EDX] & CPUID_7_0_EDX_ARCH_LBR)) {
-            const ExtSaveArea *esa = &x86_ext_save_areas[count];
-
-            *eax = esa->size;
-            *ebx = esa->offset;
-            *ecx = esa->ecx;
         } else if (count < ARRAY_SIZE(x86_ext_save_areas)) {
             const ExtSaveArea *esa = &x86_ext_save_areas[count];
 
@@ -8910,6 +8896,12 @@ static void x86_cpu_enable_xsave_components(X86CPU *cpu)
 
     mask = 0;
     for (i = 0; i < ARRAY_SIZE(x86_ext_save_areas); i++) {
+        /* Skip supervisor states if XSAVES is not supported. */
+        if (CPUID_XSTATE_XSS_MASK & (1 << i) &&
+            !(env->features[FEAT_XSAVE] & CPUID_XSAVE_XSAVES)) {
+            continue;
+        }
+
         const ExtSaveArea *esa = &x86_ext_save_areas[i];
         if (cpuid_has_xsave_feature(env, esa)) {
             mask |= (1ULL << i);
@@ -9027,11 +9019,13 @@ void x86_cpu_expand_features(X86CPU *cpu, Error **errp)
         }
     }
 
-    if (!cpu->pdcm_on_even_without_pmu) {
+    if (!cpu->enable_pmu) {
         /* PDCM is fixed1 bit for TDX */
-        if (!cpu->enable_pmu && !is_tdx_vm()) {
+        if (!cpu->pdcm_on_even_without_pmu && !is_tdx_vm()) {
             env->features[FEAT_1_ECX] &= ~CPUID_EXT_PDCM;
         }
+
+        env->features[FEAT_7_0_EDX] &= ~CPUID_7_0_EDX_ARCH_LBR;
     }
 
     for (i = 0; i < ARRAY_SIZE(feature_dependencies); i++) {