Re: [Xen-devel] [Patch] Allowing PV-OPS kernel to detect whether XSAVE is supported

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2010-11-09 at 06:22 +0000, Haitao Shan wrote:
> Hi, Jeremy,
> 
> This patch allows pv-ops kernel to detect whether XSAVE is supported
> (before masking it unconditionally through xen_cpuid).
> Can you please have review? Thanks!
> 
> Signed-off-by: Shan Haitao <haitao.shan@xxxxxxxxx>
> 
> Shan Haitao 
> 

> diff --git a/arch/x86/xen/enlighten.c b/arch/x86/xen/enlighten.c
> index fd3803e..03bfaf7 100644
> --- a/arch/x86/xen/enlighten.c
> +++ b/arch/x86/xen/enlighten.c
> @@ -252,6 +252,13 @@ static __init void xen_init_cpuid_mask(void)
>                           (1 << X86_FEATURE_MCA)  |  /* disable MCA */
>                           (1 << X86_FEATURE_APIC) |  /* disable local APIC */
>                           (1 << X86_FEATURE_ACPI));  /* disable ACPI */
> +       ax = 1;
> +       xen_cpuid(&ax, &bx, &cx, &dx);
> +
> +       /* Xen will set CR4.OSXSAVE if supported and not disabled by force */

For how long has the hypervisor had this behaviour? IIRC older
hypervisors did not correctly expose/mask the *XSAVE CPUID flags and
would causes PV guests to crash when they used *XSAVE features which
weren't actually available.

In other words have you confirmed that this patch does not break the
kernel running on older hypervisors such as Xen 4.0?


> +       if ( cx & (1 << (X86_FEATURE_XSAVE % 32)) &&
> +               cx & (1 << (X86_FEATURE_OSXSAVE % 32)) )
> +               return;
>  
>         cpuid_leaf1_ecx_mask &= ~(1 << (X86_FEATURE_XSAVE % 32)); /* disable 
> XSAVE */
>  } 


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel