forward cpuid leaves when using -cpu host

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 <[email protected]>

Quoted 2 lines

Signed-off-by Benoit Canet <[email protected]>

Reviewed-by Eduardo Habkost <[email protected]>

Quoted 4 lines

Quoted 2 lines

Signed-off-by Benoit Canet <[email protected]>

Reviewed-by Eduardo Habkost <[email protected]>

Thanks.

Do you have an idea on how QEMU could reflect the real host clock frequency to the guest when the host cpu scaling governor kicks in ? Giving a false value to cloud customers is mildly annoying.

Quoted 7 lines · Benoît Canet

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 <[email protected]>

Reviewed-by Eduardo Habkost <[email protected]>

Signature · 2 lines

-- 
Eduardo

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 <[email protected]>

---
 target-i386/cpu-qom.h |    3 +++
 target-i386/cpu.c     |   19 +++++++++++++++++++
 2 files changed, 22 insertions(+)

target-i386/cpu-qom.h +3 -0

index c4447c2..b1d1bd8 100644
@@ -70,6 +70,9 @@ typedef struct X86CPU {
     bool hyperv_relaxed_timing;
     int hyperv_spinlock_attempts;
 
+    /* if true the CPUID code directly forward host cache leaves to the guest */
+    bool fwd_host_cache_info;
+
     /* Features that were filtered out because of missing host capabilities */
     uint32_t filtered_features[FEATURE_WORDS];
 

target-i386/cpu.c +15 -0

index c36345e..f0df4db 100644
@@ -486,6 +486,7 @@ typedef struct x86_def_t {
     int stepping;
     FeatureWordArray features;
     char model_id[48];
+    bool fwd_host_cache_info;
 } x86_def_t;
 
 #define I486_FEATURES (CPUID_FP87 | CPUID_VME | CPUID_PSE)

@@ -1139,6 +1140,7 @@ static void kvm_cpu_fill_host(x86_def_t *x86_cpu_def)
     assert(kvm_enabled());
 
     x86_cpu_def->name = "host";
+    x86_cpu_def->fwd_host_cache_info = true;
     host_cpuid(0x0, 0, &eax, &ebx, &ecx, &edx);
     x86_cpu_vendor_words2str(x86_cpu_def->vendor, ebx, edx, ecx);
 

@@ -1888,6 +1890,7 @@ 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;
+    cpu->fwd_host_cache_info = def->fwd_host_cache_info;
 
     object_property_set_str(OBJECT(cpu), def->model_id, "model-id", errp);
 }

@@ -2062,6 +2065,10 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
         break;
     case 2:
         /* cache info: needed for Pentium Pro compatibility */
+        if (cpu->fwd_host_cache_info) {
+            host_cpuid(index, 0, eax, ebx, ecx, edx);
+            break;
+        }
         *eax = 1; /* Number of CPUID[EAX=2] calls required */
         *ebx = 0;
         *ecx = 0;

@@ -2071,6 +2078,10 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
         break;
     case 4:
         /* cache info: needed for Core compatibility */
+        if (cpu->fwd_host_cache_info) {
+            host_cpuid(index, count, eax, ebx, ecx, edx);
+            break;
+        }
         if (cs->nr_cores > 1) {
             *eax = (cs->nr_cores - 1) << 26;
         } else {

@@ -2228,6 +2239,10 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, uint32_t count,
         break;
     case 0x80000005:
         /* cache info (L1 cache) */
+        if (cpu->fwd_host_cache_info) {
+            host_cpuid(index, 0, eax, ebx, ecx, edx);
+            break;
+        }
         *eax = (L1_DTLB_2M_ASSOC << 24) | (L1_DTLB_2M_ENTRIES << 16) | \
                (L1_ITLB_2M_ASSOC <<  8) | (L1_ITLB_2M_ENTRIES);
         *ebx = (L1_DTLB_4K_ASSOC << 24) | (L1_DTLB_4K_ENTRIES << 16) | \