Re: [Qemu-devel] [PATCH uq/master 1/2] x86: fix migration from pre-version 12

[Gleb Natapov <gleb@redhat.com>]

On Thu, Sep 05, 2013 at 03:06:21PM +0200, Paolo Bonzini wrote:
> On KVM, the KVM_SET_XSAVE would be executed with a 0 xstate_bv,
> and not restore anything.
> 
XRSTOR restores FP/SSE state to reset state if no bits are set in
xstate_bv. This is what should happen on reset, no?

> Since FP and SSE data are always valid, set them in xstate_bv at reset
> time.  In fact, that value is the same that KVM_GET_XSAVE returns on
> pre-XSAVE hosts.
It is needed for migration between non xsave host to xsave host.

> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  target-i386/cpu.c | 1 +
>  target-i386/cpu.h | 5 +++++
>  2 files changed, 6 insertions(+)
> 
> diff --git a/target-i386/cpu.c b/target-i386/cpu.c
> index c36345e..ac83106 100644
> --- a/target-i386/cpu.c
> +++ b/target-i386/cpu.c
> @@ -2386,6 +2386,7 @@ static void x86_cpu_reset(CPUState *s)
>      env->fpuc = 0x37f;
>  
>      env->mxcsr = 0x1f80;
> +    env->xstate_bv = XSTATE_FP | XSTATE_SSE;
>  
>      env->pat = 0x0007040600070406ULL;
>      env->msr_ia32_misc_enable = MSR_IA32_MISC_ENABLE_DEFAULT;
> diff --git a/target-i386/cpu.h b/target-i386/cpu.h
> index 5723eff..a153078 100644
> --- a/target-i386/cpu.h
> +++ b/target-i386/cpu.h
> @@ -380,6 +380,11 @@
>  
>  #define MSR_VM_HSAVE_PA                 0xc0010117
>  
> +#define XSTATE_SUPPORTED		(XSTATE_FP|XSTATE_SSE|XSTATE_YMM)
Supported by whom? By QEMU? We should filer unsupported bits from CPUID.0D then too.

> +#define XSTATE_FP			1
> +#define XSTATE_SSE			2
> +#define XSTATE_YMM			4
> +
>  /* CPUID feature words */
>  typedef enum FeatureWord {
>      FEAT_1_EDX,         /* CPUID[1].EDX */
> -- 
> 1.8.3.1
> 

--
			Gleb.