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

To: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH 2/4] XSAVE/XRSTOR: enable guest save/restore
From: Weidong Han <weidong.han@xxxxxxxxx>
Date: Tue, 31 Aug 2010 20:28:09 +0800
Cc: Jeremy Fitzhardinge <jeremy@xxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxxxx>
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Keir Fraser wrote:
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

I will send out other patches soon, and revise this patch later.

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