Re: [Xen-devel] [PATCH] Fix PV CPUID virtualization of XSave

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 16.09.11 at 02:46, Haitao Shan <maillists.shan@xxxxxxxxx> wrote:
> Hi, Keir,
> 
> The patch will fix XSave CPUID virtualization for PV guests. The XSave
> area size returned by CPUID leaf D is changed dynamically depending on
> the XCR0. Tools/libxc only assigns a static value. The fix will adjust
> xsave area size during runtime.
> 
> Note: This fix is already in HVM cpuid virtualization. And Dom0 is not
> affected, either.
> 
> Signed-off-by:  Shan Haitao <haitao.shan@xxxxxxxxx>
> 
> Shan Haitao
> 
> diff -r 5fe770c8a8a3 xen/arch/x86/traps.c
> --- a/xen/arch/x86/traps.c    Tue Sep 06 15:49:40 2011 +0100
> +++ b/xen/arch/x86/traps.c    Wed Sep 07 02:09:12 2011 +0800
> @@ -770,6 +770,30 @@ static void pv_cpuid(struct cpu_user_reg
>      {
>          if ( !cpuid_hypervisor_leaves(a, c, &a, &b, &c, &d) )
>              domain_cpuid(current->domain, a, c, &a, &b, &c, &d);
> +
> +        switch ( a )
> +        {
> +        case 0xd:
> +        {
> +            unsigned int sub_leaf, _eax, _ebx, _ecx, _edx;
> +            /* EBX value of main leaf 0 depends on enabled xsave features 
> */
> +            if ( c == 0 && current->arch.xcr0 )
> +            {
> +                /* reset EBX to default value first */
> +                b = XSTATE_AREA_MIN_SIZE;
> +                for ( sub_leaf = 2; sub_leaf < 64; sub_leaf++ )

Shouldn't the upper bound be 63 here (as bit 63 serves a different
purpose, and if that bit was set code changes would be required in
various other places)?

Jan

> +                {
> +                    if ( !(current->arch.xcr0 & (1ULL << sub_leaf)) )
> +                        continue;
> +                    domain_cpuid(current->domain, a, c, &_eax, &_ebx, &_ecx,
> +                                 &_edx);
> +                    if ( (_eax + _ebx) > b )
> +                        b = _eax + _ebx;
> +                }
> +            }
> +        break;
> +        }
> +        }
>          goto out;
>      }




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