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

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 18.11.14 at 16:26, <dkoch@xxxxxxxxxxx> 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.

This needs more explanation: xcr0_accum is named this way
because bits never disappear from it. Hence afaics any piece of
the xsave area ever having got written with a non-zero value
would be part of the data actually used on migration.

> --- 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

Even if we really have to go this route, you should recall the
discussion on the earlier patch of yours: The end result should
not be that two messages get logged for a single event.

Jan


_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxx
http://lists.xen.org/xen-devel