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Re: [Qemu-devel] [PATCH 1/3] qemu-kvm: Invert svm-flag setting logic


From: Alexander Graf
Subject: Re: [Qemu-devel] [PATCH 1/3] qemu-kvm: Invert svm-flag setting logic
Date: Tue, 7 Sep 2010 14:23:55 +0200

On 07.09.2010, at 13:27, Joerg Roedel wrote:

> This patch changes the setting logic for the svm bit in
> qemu-kvm. The bit is now explicitly set on -enable-nesting
> instead of masked out if the parameter is not supplied.
> 
> Signed-off-by: Joerg Roedel <address@hidden>
> ---
> target-i386/cpuid.c |   12 ++++++------
> 1 files changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/target-i386/cpuid.c b/target-i386/cpuid.c
> index d63fdcb..5fa0dd0 100644
> --- a/target-i386/cpuid.c
> +++ b/target-i386/cpuid.c
> @@ -276,8 +276,8 @@ static x86_def_t builtin_x86_defs[] = {
>         .ext_features = CPUID_EXT_SSE3 | CPUID_EXT_CX16 | CPUID_EXT_POPCNT,
>         .ext2_features = (PPRO_FEATURES & EXT2_FEATURE_MASK) |
>             CPUID_EXT2_LM | CPUID_EXT2_SYSCALL | CPUID_EXT2_NX,
> -        .ext3_features = CPUID_EXT3_LAHF_LM | CPUID_EXT3_SVM |
> -            CPUID_EXT3_ABM | CPUID_EXT3_SSE4A,
> +        .ext3_features = CPUID_EXT3_LAHF_LM | CPUID_EXT3_ABM |
> +                         CPUID_EXT3_SSE4A,
>         .xlevel = 0x8000000A,
>         .model_id = "QEMU Virtual CPU version " QEMU_VERSION,
>     },
> @@ -303,8 +303,8 @@ static x86_def_t builtin_x86_defs[] = {
>                     CPUID_EXT3_CR8LEG,
>                     CPUID_EXT3_MISALIGNSSE, CPUID_EXT3_3DNOWPREFETCH,
>                     CPUID_EXT3_OSVW, CPUID_EXT3_IBS */
> -        .ext3_features = CPUID_EXT3_LAHF_LM | CPUID_EXT3_SVM |
> -            CPUID_EXT3_ABM | CPUID_EXT3_SSE4A,
> +        .ext3_features = CPUID_EXT3_LAHF_LM | CPUID_EXT3_ABM |
> +                         CPUID_EXT3_SSE4A,
>         .xlevel = 0x8000001A,
>         .model_id = "AMD Phenom(tm) 9550 Quad-Core Processor"
>     },
> @@ -1154,8 +1154,8 @@ void cpu_x86_cpuid(CPUX86State *env, uint32_t index, 
> uint32_t count,
>             /* disable CPU features that KVM cannot support */
> 
>             /* svm */
> -            if (!kvm_nested)
> -                *ecx &= ~CPUID_EXT3_SVM;
> +            if (kvm_nested)

I think we should get rid of kvm_nested and -enable-nesting. Instead, we should 
enable the SVM bit in the "host" and "qemu64" cpu types, but not in "kvm64". 
This way users are safe to not use nested svm, but can choose to do so if they 
like.

Also, it should be possible to do something like -cpu kvm64,flags=+svm. Without 
having to mess with -enable-nesting.


Alex




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