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Re: [libvirt] [PATCH qom-cpu 03/11] target-i386: kvm: -cpu host: Use GET_SUPPORTED_CPUID for SVM features



On Fri, Jan 04, 2013 at 08:01:04PM -0200, Eduardo Habkost wrote:
> The existing -cpu host code simply set every bit inside svm_features
> (initializing it to -1), and that makes it impossible to make the
> enforce/check options work properly when the user asks for SVM features
> explicitly in the command-line.
> 
> So, instead of initializing svm_features to -1, use GET_SUPPORTED_CPUID
> to fill only the bits that are supported by the host (just like we do
> for all other CPUID feature words inside kvm_cpu_fill_host()).
> 
> This will keep the existing behavior (as filter_features_for_kvm()
> already uses GET_SUPPORTED_CPUID to filter svm_features), but will allow
> us to properly check for KVM features inside
> kvm_check_features_against_host() later.
> 
> For example, we will be able to make this:
> 
>   $ qemu-system-x86_64 -cpu ...,+pfthreshold,enforce
> 
> refuse to start if the SVM "pfthreshold" feature is not supported by the
> host (after we fix kvm_check_features_against_host() to check SVM flags
> as well).
> 
> Signed-off-by: Eduardo Habkost <ehabkost redhat com>
Reviewed-by: Gleb Natapov <gleb redhat com>

> ---
> Changes v2:
>  - Coding style (indentation) fix
> 
> Cc: Gleb Natapov <gleb redhat com>
> Cc: Marcelo Tosatti <mtosatti redhat com>
> Cc: Joerg Roedel <joro 8bytes org>
> Cc: kvm vger kernel org
> ---
>  target-i386/cpu.c | 11 ++++-------
>  1 file changed, 4 insertions(+), 7 deletions(-)
> 
> diff --git a/target-i386/cpu.c b/target-i386/cpu.c
> index c83a566..c49a97c 100644
> --- a/target-i386/cpu.c
> +++ b/target-i386/cpu.c
> @@ -908,13 +908,10 @@ static void kvm_cpu_fill_host(x86_def_t *x86_cpu_def)
>          }
>      }
>  
> -    /*
> -     * Every SVM feature requires emulation support in KVM - so we can't just
> -     * read the host features here. KVM might even support SVM features not
> -     * available on the host hardware. Just set all bits and mask out the
> -     * unsupported ones later.
> -     */
> -    x86_cpu_def->svm_features = -1;
> +    /* Other KVM-specific feature fields: */
> +    x86_cpu_def->svm_features =
> +        kvm_arch_get_supported_cpuid(s, 0x8000000A, 0, R_EDX);
> +
>  #endif /* CONFIG_KVM */
>  }
>  
> -- 
> 1.7.11.7

--
			Gleb.


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