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

[Igor Mammedov <imammedo@redhat.com>]

On Thu, 3 Oct 2013 13:01:54 +0300
Gleb Natapov <gleb@redhat.com> wrote:

> On Thu, Oct 03, 2013 at 11:59:24AM +0200, Igor Mammedov wrote:
> > On Wed,  2 Oct 2013 17:54:57 +0200
> > Paolo Bonzini <pbonzini@redhat.com> 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 <pbonzini@redhat.com>
> > > ---
> > >  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.

Ah, I'm sorry for noise. I've not noticed it in previous hunk.

> 
> > 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.
>