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

[Eduardo Habkost]

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:

        /*
         * 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