[Qemu-devel] [PATCH] i386: forward CPUID cache leaves when -cpu host is used

["Benoît Canet" <benoit@irqsave.net>]

Some users running cpu intensive tasks checking the cache CPUID leaves at
startup and making decisions based on the result reported that the guest was
not reflecting the host CPUID leaves when -cpu host is used.

This patch fix this.

Signed-off-by: Benoit Canet <benoit@irqsave.net>
---
 target-i386/cpu.c |   19 +++++++++++++++++++
 target-i386/cpu.h |    1 +
 2 files changed, 20 insertions(+)

diff --git a/target-i386/cpu.c b/target-i386/cpu.c
index 42c5de0..2c8eaf7 100644
--- a/target-i386/cpu.c
+++ b/target-i386/cpu.c
@@ -374,6 +374,7 @@ typedef struct x86_def_t {
     int stepping;
     FeatureWordArray features;
     char model_id[48];
+    bool fwd_cpuid_cache_leaves;
 } x86_def_t;
 
 #define I486_FEATURES (CPUID_FP87 | CPUID_VME | CPUID_PSE)
@@ -1027,6 +1028,7 @@ static void kvm_cpu_fill_host(x86_def_t *x86_cpu_def)
     assert(kvm_enabled());
 
     x86_cpu_def->name = "host";
+    x86_cpu_def->fwd_cpuid_cache_leaves = true;
     host_cpuid(0x0, 0, &eax, &ebx, &ecx, &edx);
     x86_cpu_vendor_words2str(x86_cpu_def->vendor, ebx, edx, ecx);
 
@@ -1776,6 +1778,7 @@ static void cpu_x86_register(X86CPU *cpu, const char *name, Error **errp)
     env->features[FEAT_C000_0001_EDX] = def->features[FEAT_C000_0001_EDX];
     env->features[FEAT_7_0_EBX] = def->features[FEAT_7_0_EBX];
     env->cpuid_xlevel2 = def->xlevel2;
+    env->fwd_cpuid_cache_leaves = def->fwd_cpuid_cache_leaves;
 
     object_property_set_str(OBJECT(cpu), def->model_id, "model-id", errp);
 }
@@ -1949,6 +1952,10 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
         }
         break;
     case 2:
+        if (env->fwd_cpuid_cache_leaves) {
+            host_cpuid(0x2, 0, eax, ebx, ecx, edx);
+            break;
+        }
         /* cache info: needed for Pentium Pro compatibility */
         *eax = 1;
         *ebx = 0;
@@ -1956,6 +1963,10 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
         *edx = 0x2c307d;
         break;
     case 4:
+        if (env->fwd_cpuid_cache_leaves) {
+            host_cpuid(0x4, count, eax, ebx, ecx, edx);
+            break;
+        }
         /* cache info: needed for Core compatibility */
         if (cs->nr_cores > 1) {
             *eax = (cs->nr_cores - 1) << 26;
@@ -2102,6 +2113,10 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
         break;
     case 0x80000005:
         /* cache info (L1 cache) */
+        if (env->fwd_cpuid_cache_leaves) {
+            host_cpuid(0x80000005, 0, eax, ebx, ecx, edx);
+            break;
+        }
         *eax = 0x01ff01ff;
         *ebx = 0x01ff01ff;
         *ecx = 0x40020140;
@@ -2109,6 +2124,10 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
         break;
     case 0x80000006:
         /* cache info (L2 cache) */
+        if (env->fwd_cpuid_cache_leaves) {
+            host_cpuid(0x80000006, 0, eax, ebx, ecx, edx);
+            break;
+        }
         *eax = 0;
         *ebx = 0x42004200;
         *ecx = 0x02008140;
diff --git a/target-i386/cpu.h b/target-i386/cpu.h
index 8a3d0fd..1ec32fa 100644
--- a/target-i386/cpu.h
+++ b/target-i386/cpu.h
@@ -865,6 +865,7 @@ typedef struct CPUX86State {
     bool tsc_valid;
     int tsc_khz;
     void *kvm_xsave_buf;
+    bool fwd_cpuid_cache_leaves;
 
     /* in order to simplify APIC support, we leave this pointer to the
        user */
-- 
1.7.10.4