[Qemu-devel] [PATCH] target-i386: warns users when CPU threads>1 for AMD CPUs

[Wei Huang]

No AMD CPUs support hyperthreading. When users select threads>1 in
-smp option, QEMU fixes it by adjusting CPUID_0000_0001_EBX and
CPUID_8000_0008_ECX based on inputs (sockets, cores, threads);
so guest VM can boot correctly. However it is still better to gives
users a warning when such case happens.

Signed-off-by: Wei Huang <address@hidden>
---
 target-i386/cpu.c | 23 ++++++++++++++++++++---
 1 file changed, 20 insertions(+), 3 deletions(-)

diff --git a/target-i386/cpu.c b/target-i386/cpu.c
index e7bf9de..84cbbcd 100644
--- a/target-i386/cpu.c
+++ b/target-i386/cpu.c
@@ -2696,6 +2696,10 @@ static void x86_cpu_apic_realize(X86CPU *cpu, Error 
**errp)
 }
 #endif
 
+
+#define IS_AMD_CPU(env) ((env)->cpuid_vendor1 == CPUID_VENDOR_AMD_1 && \
+                         (env)->cpuid_vendor2 == CPUID_VENDOR_AMD_2 && \
+                         (env)->cpuid_vendor3 == CPUID_VENDOR_AMD_3)
 static void x86_cpu_realizefn(DeviceState *dev, Error **errp)
 {
     CPUState *cs = CPU(dev);
@@ -2703,6 +2707,7 @@ static void x86_cpu_realizefn(DeviceState *dev, Error 
**errp)
     X86CPUClass *xcc = X86_CPU_GET_CLASS(dev);
     CPUX86State *env = &cpu->env;
     Error *local_err = NULL;
+    static bool ht_warned;
 
     if (env->features[FEAT_7_0_EBX] && env->cpuid_level < 7) {
         env->cpuid_level = 7;
@@ -2711,9 +2716,7 @@ static void x86_cpu_realizefn(DeviceState *dev, Error 
**errp)
     /* On AMD CPUs, some CPUID[8000_0001].EDX bits must match the bits on
      * CPUID[1].EDX.
      */
-    if (env->cpuid_vendor1 == CPUID_VENDOR_AMD_1 &&
-        env->cpuid_vendor2 == CPUID_VENDOR_AMD_2 &&
-        env->cpuid_vendor3 == CPUID_VENDOR_AMD_3) {
+    if (IS_AMD_CPU(env)) {
         env->features[FEAT_8000_0001_EDX] &= ~CPUID_EXT2_AMD_ALIASES;
         env->features[FEAT_8000_0001_EDX] |= (env->features[FEAT_1_EDX]
            & CPUID_EXT2_AMD_ALIASES);
@@ -2742,6 +2745,20 @@ static void x86_cpu_realizefn(DeviceState *dev, Error 
**errp)
     mce_init(cpu);
     qemu_init_vcpu(cs);
 
+    /* AMD CPU doesn't support hyperthreading. Even though QEMU fixes
+     * this issue by adjusting CPUID_0000_0001_EBX and CPUID_8000_0008_ECX
+     * based on inputs (sockets,cores,threads), it is still better to gives
+     * users a warning.
+     *
+     * NOTE: the following code has to follow qemu_init_vcpu(). Otherwise
+     * cs->nr_threads hasn't be populated yet and the checking is incorrect.
+     */
+    if (IS_AMD_CPU(env) && (cs->nr_threads > 1) && !ht_warned) {
+        error_report("AMD CPU doesn't support hyperthreading. Please configure"
+                     " -smp options properly.");
+        ht_warned = true;
+    }
+
     x86_cpu_apic_realize(cpu, &local_err);
     if (local_err != NULL) {
         goto out;
-- 
1.8.3.1