Re: [Qemu-devel] [PATCH v3 uq/master 2/2] x86: cpuid: reconstruct leaf 0Dh data

[Gleb Natapov]

On Thu, Oct 03, 2013 at 11:59:24AM +0200, Igor Mammedov wrote:
> On Wed,  2 Oct 2013 17:54:57 +0200
> Paolo Bonzini <address@hidden> wrote:
> 
> > The data in leaf 0Dh depends on information from other feature bits.
> > Instead of passing it blindly from the host, compute it based on
> > whether these feature bits are enabled.
> > 
> > Signed-off-by: Paolo Bonzini <address@hidden>
> > ---
> >  target-i386/cpu.c | 65 
> > ++++++++++++++++++++++++++++++++++++++++---------------
> >  1 file changed, 48 insertions(+), 17 deletions(-)
> > 
> > diff --git a/target-i386/cpu.c b/target-i386/cpu.c
> > index ac83106..1addb18 100644
> > --- a/target-i386/cpu.c
> > +++ b/target-i386/cpu.c
> > @@ -328,6 +328,15 @@ X86RegisterInfo32 x86_reg_info_32[CPU_NB_REGS32] = {
> >  };
> >  #undef REGISTER
> >  
> > +typedef struct ExtSaveArea {
> > +    uint32_t feature, bits;
> > +    uint32_t offset, size;
> > +} ExtSaveArea;
> > +
> > +static const ExtSaveArea ext_save_areas[] = {
> > +    [2] = { .feature = FEAT_1_ECX, .bits = CPUID_EXT_AVX,
> > +            .offset = 0x100, .size = 0x240 },
> > +};
> >  
> >  const char *get_register_name_32(unsigned int reg)
> >  {
> > @@ -2169,29 +2178,51 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t 
> > index, uint32_t count,
> >              *edx = 0;
> >          }
> >          break;
> > -    case 0xD:
> > +    case 0xD: {
> > +        KVMState *s = cs->kvm_state;
> > +        uint64_t kvm_mask;
> > +        int i;
> > +
> >          /* Processor Extended State */
> > -        if (!(env->features[FEAT_1_ECX] & CPUID_EXT_XSAVE)) {
> > -            *eax = 0;
> > -            *ebx = 0;
> > -            *ecx = 0;
> > -            *edx = 0;
> > +        *eax = 0;
> > +        *ebx = 0;
> > +        *ecx = 0;
> > +        *edx = 0;
> > +        if (!(env->features[FEAT_1_ECX] & CPUID_EXT_XSAVE) || 
> > !kvm_enabled()) {
> >              break;
> >          }
> > -        if (kvm_enabled()) {
> > -            KVMState *s = cs->kvm_state;
> > +        kvm_mask =
> > +            kvm_arch_get_supported_cpuid(s, 0xd, 0, R_EAX) |
> > +            ((uint64_t)kvm_arch_get_supported_cpuid(s, 0xd, 0, R_EDX) << 
> > 32);
> calling kvm_arch_get_supported_cpuid() without kvm_enabled() guard
> could regress TCG mode on non KVM host:
> 
But there is kvm_enabled() guard above.

> kvm_arch_get_supported_cpuid -> get_supported_cpuid -> try_get_cpuid ->
>        r = kvm_ioctl(s, KVM_GET_SUPPORTED_CPUID, cpuid);
>        ...
>        if (r < 0) {
>         if (r == -E2BIG) {
>             g_free(cpuid);
>             return NULL;
>         } else {
>             fprintf(stderr, "KVM_GET_SUPPORTED_CPUID failed: %s\n",
>                     strerror(-r));
>             exit(1);
>             ^^^^^^^^^ guest suddenly dies
> 
> >  
> > -            *eax = kvm_arch_get_supported_cpuid(s, 0xd, count, R_EAX);
> > -            *ebx = kvm_arch_get_supported_cpuid(s, 0xd, count, R_EBX);
> > -            *ecx = kvm_arch_get_supported_cpuid(s, 0xd, count, R_ECX);
> > -            *edx = kvm_arch_get_supported_cpuid(s, 0xd, count, R_EDX);
> > -        } else {
> > -            *eax = 0;
> > -            *ebx = 0;
> > -            *ecx = 0;
> > -            *edx = 0;
> > +        if (count == 0) {
> > +            *ecx = 0x240;
> > +            for (i = 2; i < ARRAY_SIZE(ext_save_areas); i++) {
> > +                const ExtSaveArea *esa = &ext_save_areas[i];
> > +                if ((env->features[esa->feature] & esa->bits) == esa->bits 
> > &&
> > +                    (kvm_mask & (1 << i)) != 0) {
> > +                    if (i < 32) {
> > +                        *eax |= 1 << i;
> > +                    } else {
> > +                        *edx |= 1 << (i - 32);
> > +                    }
> > +                    *ecx = MAX(*ecx, esa->offset + esa->size);
> > +                }
> > +            }
> > +            *eax |= kvm_mask & (XSTATE_FP | XSTATE_SSE);
> > +            *ebx = *ecx;
> > +        } else if (count == 1) {
> > +            *eax = kvm_arch_get_supported_cpuid(s, 0xd, 1, R_EAX);
> > +        } else if (count < ARRAY_SIZE(ext_save_areas)) {
> > +            const ExtSaveArea *esa = &ext_save_areas[count];
> > +            if ((env->features[esa->feature] & esa->bits) == esa->bits &&
> > +                (kvm_mask & (1 << count)) != 0) {
> > +                *eax = esa->offset;
> > +                *ebx = esa->size;
> > +            }
> >          }
> >          break;
> > +    }
> >      case 0x80000000:
> >          *eax = env->cpuid_xlevel;
> >          *ebx = env->cpuid_vendor1;

--
                        Gleb.