Re: [Qemu-devel] [PATCH v14 1/6] i386: Set TOPOEXT unconditionally for comapatibility

[Moger, Babu]

> -----Original Message-----
> From: Eduardo Habkost [mailto:address@hidden
> Sent: Wednesday, June 13, 2018 9:22 PM
> To: Moger, Babu <address@hidden>
> Cc: address@hidden; address@hidden; address@hidden;
> address@hidden; address@hidden; address@hidden;
> address@hidden; address@hidden; address@hidden
> Subject: Re: [PATCH v14 1/6] i386: Set TOPOEXT unconditionally for
> comapatibility
> 
> On Wed, Jun 13, 2018 at 09:18:22PM -0400, Babu Moger wrote:
> > Enabling TOPOEXT feature might cause compatibility issues if
> > older kernels does not set this feature. Lets set this feature
> > unconditionally.
> >
> > Signed-off-by: Babu Moger <address@hidden>
> > ---
> >  target/i386/kvm.c | 6 ++++++
> >  1 file changed, 6 insertions(+)
> >
> > diff --git a/target/i386/kvm.c b/target/i386/kvm.c
> > index 445e0e0..6f2cca7 100644
> > --- a/target/i386/kvm.c
> > +++ b/target/i386/kvm.c
> > @@ -372,6 +372,12 @@ uint32_t
> kvm_arch_get_supported_cpuid(KVMState *s, uint32_t function,
> >          if (host_tsx_blacklisted()) {
> >              ret &= ~(CPUID_7_0_EBX_RTM | CPUID_7_0_EBX_HLE);
> >          }
> > +    } else if (function == 0x80000001 && reg == R_ECX) {
> > +        /* Enabling topoext feature might cause compatibility issues if
> > +         * older kernel does not set this feature. Lets set this feature
> > +         * unconditionally.
> > +         */
> 
> Thanks.  I will apply and rewrite the comment as:
Sure. Thanks
> 
>         /*
>          * It's safe to enable TOPOEXT even if it's not returned
>          * by GET_SUPPORTED_CPUID.  Unconditionally enabling
>          * TOPOEXT here let us keep CPU models runnable on
>          * older kernels even when TOPOEXT is enabled.
>          */
> 
> > +        ret |= CPUID_EXT3_TOPOEXT;
> >      } else if (function == 0x80000001 && reg == R_EDX) {
> >          /* On Intel, kvm returns cpuid according to the Intel spec,
> >           * so add missing bits according to the AMD spec:
> > --
> > 1.8.3.1
> >
> 
> --
> Eduardo