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Re: [Xen-devel] [PATCH 2/4] XSAVE/XRSTOR: enable guest save/restore

To: Jan Beulich <JBeulich@xxxxxxxxxx>, Weidong Han <weidong.han@xxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH 2/4] XSAVE/XRSTOR: enable guest save/restore
From: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date: Tue, 31 Aug 2010 08:30:51 +0100
Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>
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On 31/08/2010 08:08, "Jan Beulich" <JBeulich@xxxxxxxxxx> wrote:

>> #define VGCF_I387_VALID                (1<<0)
>> #define VGCF_IN_KERNEL                 (1<<2)
>> #define _VGCF_i387_valid               0
> As Keir already indicated, you can't change the size of this structure.
> I'd say that it was a mistake to include the FPU state directly here in
> the first place - you'll have to invent a mechanism to (compatibly)
> not make this a requirement anymore. E.g. use the reserved part of
> fpu_ctxt to store a guest handle referring to the actual area: This
> ought to work as (iirc) the structure is used as input only
> (VCPUOP_initialize) outside of the tools, and the domctl interface is
> allowed to change as long as you don't break compatibility with
> stored data (saved guest images).

I would agree but for the fact that it appears that XSAVE is only supported
for HVM guests right now. Hence this whole rigmarole is actually currently
pointless, since HVM guests do not initialise/save/restore the
vcpu_guest_context structure. I think probably this bit of the patch could
simply be dropped until PV support is added.

 -- Keir

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