Re: [Qemu-devel] [PATCH v2 3/5] target/i386: Add support for CPUID_8000_001E for AMD

[Moger, Babu]

> -----Original Message-----
> From: Radim Krčmář [mailto:address@hidden
> Sent: Thursday, March 1, 2018 1:57 PM
> To: Moger, Babu <address@hidden>
> Cc: address@hidden; address@hidden; address@hidden;
> address@hidden; address@hidden; address@hidden;
> address@hidden; Hook, Gary <address@hidden>
> Subject: Re: [PATCH v2 3/5] target/i386: Add support for CPUID_8000_001E
> for AMD
> 
> 2018-02-28 22:18+0000, Moger, Babu:
> > > -----Original Message-----
> > > From: Radim Krčmář [mailto:address@hidden
> > > Sent: Wednesday, February 28, 2018 12:24 PM
> > > To: Moger, Babu <address@hidden>
> > > Cc: address@hidden; address@hidden; address@hidden;
> > > address@hidden; address@hidden; address@hidden;
> > > address@hidden; Hook, Gary <address@hidden>
> > > Subject: Re: [PATCH v2 3/5] target/i386: Add support for
> CPUID_8000_001E
> > > for AMD
> > >
> > > 2018-02-23 21:30-0500, Babu Moger:
> > > > From: Stanislav Lanci <address@hidden>
> > > >
> > > > Populate threads/core_id/apic_ids/socket_id when
> CPUID_EXT3_TOPOEXT
> > > > feature is supported. This is required to support hyperthreading
> > > > feature on AMD CPUS. These are supported via CPUID_8000_001E
> > > extended
> > > > functions.
> > > >
> > > > Signed-off-by: Stanislav Lanci <address@hidden>
> > > > Signed-off-by: Babu Moger <address@hidden>
> > > > ---
> > > >  target/i386/cpu.c | 8 ++++++++
> > > >  1 file changed, 8 insertions(+)
> > > >
> > > > diff --git a/target/i386/cpu.c b/target/i386/cpu.c
> > > > index a5a480e..191e850 100644
> > > > --- a/target/i386/cpu.c
> > > > +++ b/target/i386/cpu.c
> > > > @@ -3666,6 +3666,14 @@ void cpu_x86_cpuid(CPUX86State *env,
> > > uint32_t index, uint32_t count,
> > > >              *edx = 0;
> > > >          }
> > > >          break;
> > > > +    case 0x8000001E:
> > > > +        if (env->features[FEAT_8000_0001_ECX] &
> CPUID_EXT3_TOPOEXT) {
> > > > +            *eax = cpu->apic_id;
> > > > +            *ebx = (cs->nr_threads - 1) << 8 | cpu->core_id;
> > >
> > > Do we somewhere assert that AMD cannot have cpu->core_id > 255?
> > > (qemu does allow weird configurations.)
> >
> > I don't see specific assert on core_id.   But, I see that qemu does not 
> > allow
> nr_cores more than 255.
> > Also I see that core_id is iterated based on nr_cores.  If you strongly
> believe we need to add assert here, I will add it.
> > Let me know.
> 
> A user can emulate AMD with x2apic and intel-iommu to allow more than
> 255 vcpus and all of them can be a separate core (or its own socket),
> which would overflow this (or the next counter).
> 
> Forbidding that crazy configuration may be preferable, but an assert
> won't hurt now,

Ok. Sure. Will add assert.

> 
> thanks.
> 
> > > Thanks.
> > >
> > > > +            *ecx = cpu->socket_id;
> > > > +            *edx = 0;
> > > > +        }
> > > > +        break;
> > > >      case 0xC0000000:
> > > >          *eax = env->cpuid_xlevel2;
> > > >          *ebx = 0;
> > > > --
> > > > 1.8.3.1
> > > >
>