[Qemu-devel] [PATCH] forward cpuid leaves when using -cpu host

[Qemu-devel] [PATCH] forward cpuid leaves when using -cpu host

[Benoît Canet]

This patch uses directly cpuid_host to forward the informations instead of
storing a variable number of leaves in the cpu states.

Benoît Canet (1):
  i386: forward CPUID cache leaves when -cpu host is used

 target-i386/cpu.c |   19 +++++++++++++++++++
 target-i386/cpu.h |    1 +
 2 files changed, 20 insertions(+)

-- 
1.7.10.4

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

[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 <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

Re: [Qemu-devel] [PATCH] forward cpuid leaves when using -cpu host

[Benoît Canet]

Ping,

I am aware that this patch must be a QObject/CPUState monstruosity but I don't
see how I could store the fact that the cpu derive from a "host" type cpu.
The alternative would be to remember a variable number of leaves and serving
them to the guest as needed but I don't find that much cleaner.

Best regards

Benoît

> Le Tuesday 27 Aug 2013 à 22:38:25 (+0200), Benoît Canet a écrit :
> This patch uses directly cpuid_host to forward the informations instead of
> storing a variable number of leaves in the cpu states.
> 
> Benoît Canet (1):
>   i386: forward CPUID cache leaves when -cpu host is used
> 
>  target-i386/cpu.c |   19 +++++++++++++++++++
>  target-i386/cpu.h |    1 +
>  2 files changed, 20 insertions(+)
> 
> -- 
> 1.7.10.4
> 

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

[Andreas Färber]

Hi,

"target-i386:" please.

Am 27.08.2013 22:38, schrieb 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 <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;

This hunk may trivially conflict with Eduardo's cache flags cleanup.

> 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 */

Please place the field in X86CPU instead and document it.

Otherwise patch looks okay to me on a brief sight; but since this is
about -cpu host I would prefer this to go through uq/master once fixed
or at least to get some acks.

Regards,
Andreas

-- 
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg, Germany
GF: Jeff Hawn, Jennifer Guild, Felix Imendörffer; HRB 16746 AG Nürnberg

Re: [Qemu-devel] [PATCH] forward cpuid leaves when using -cpu host

[Eduardo Habkost]

On Mon, Sep 02, 2013 at 02:45:48PM +0200, Benoît Canet wrote:
> 
> Ping,
> 
> I am aware that this patch must be a QObject/CPUState monstruosity but I don't
> see how I could store the fact that the cpu derive from a "host" type cpu.
> The alternative would be to remember a variable number of leaves and serving
> them to the guest as needed but I don't find that much cleaner.

The idea makes sense for -cpu host, and it is not intrusive for all
other CPU models.  I just didn't take the time to look at the code to
send my "reviewed-by:" line yet. I plan to take a look today or
tomorrow.

> 
> Best regards
> 
> Benoît
> 
> > Le Tuesday 27 Aug 2013 à 22:38:25 (+0200), Benoît Canet a écrit :
> > This patch uses directly cpuid_host to forward the informations instead of
> > storing a variable number of leaves in the cpu states.
> > 
> > Benoît Canet (1):
> >   i386: forward CPUID cache leaves when -cpu host is used
> > 
> >  target-i386/cpu.c |   19 +++++++++++++++++++
> >  target-i386/cpu.h |    1 +
> >  2 files changed, 20 insertions(+)
> > 
> > -- 
> > 1.7.10.4
> > 

-- 
Eduardo

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

[Eduardo Habkost]

On Mon, Sep 02, 2013 at 02:55:36PM +0200, Andreas Färber wrote:
[...]
> > 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 */
> 
> Please place the field in X86CPU instead and document it.

While moving it, I believe the name can be made clearer. I would name it
"fwd_host_cache_info" or something like that, to make it clear that it
will expose the _host CPU_ cache information to the guest.

-- 
Eduardo