Re: [Xen-devel] [for-xen-4.5 PATCH] Ignore non-zero data in unused xsave area.

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

On Tue, Nov 18, 2014 at 10:26:31AM -0500, Don Koch wrote:
> If we restore an xsave area from an older xen that has a larger
> size than the xcr0 bit call for, it is possible to have non-zero
> data in the unused area if an xsave has ever been done that used
> that area (e.g. during a context switch). Since the vcpu's xsave
> area is never zeroed after the initial allocation, that data is
> still there. Since we are told that said area was not written to
> during the save or migration, there is no need to restore it.
> 
> Signed-off-by: Don Koch <dkoch@xxxxxxxxxxx>
> ---
> Turns out the assertion that the unused xsave area is zero
> is wrong. Unfortunately, that leaves the following as the
> only way I can think of to work around it (and is no worse
> than xsave/xrestore during context switches). Alternate
> suggestions welcome.

This is Xen 4.5 material I presume.

> 
>  xen/arch/x86/hvm/hvm.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/xen/arch/x86/hvm/hvm.c b/xen/arch/x86/hvm/hvm.c
> index 8f49b44..b2c0bc4 100644
> --- a/xen/arch/x86/hvm/hvm.c
> +++ b/xen/arch/x86/hvm/hvm.c
> @@ -2044,7 +2044,7 @@ static int hvm_load_cpu_xsave_states(struct domain *d, 
> hvm_domain_context_t *h)
>                  printk(XENLOG_G_WARNING
>                         "HVM%d.%u restore mismatch: xsave length %#x > %#x 
> (non-zero data at %#x)\n",
>                         d->domain_id, vcpuid, desc->length, size, i);
> -                return -EOPNOTSUPP;
> +                break;
>              }
>          }
>          printk(XENLOG_G_WARNING
> -- 
> 1.8.3.1
> 
> 
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