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Re: [Xen-devel] [PATCH 0/3 v2] XSAVE/XRSTOR fixes and enhancements

To: Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Subject: Re: [Xen-devel] [PATCH 0/3 v2] XSAVE/XRSTOR fixes and enhancements
From: Weidong Han <weidong.han@xxxxxxxxx>
Date: Wed, 01 Sep 2010 16:26:50 +0800
Cc: Tim Deegan <Tim.Deegan@xxxxxxxxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxx>, Jan Beulich <JBeulich@xxxxxxxxxx>
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Keir Fraser wrote:
On 01/09/2010 08:56, "Weidong Han" <weidong.han@xxxxxxxxx> wrote:

Well that's how it was explained to me at the time. Was that in fact wrong
and we are already broken for save/restore for some subtle unexplained
When XSAVE is enabled, it saves states to xsave_area in struct hvm_vcpu.
But hvm_save_cpu_ctxt and hvm_load_cpu_ctxt don't save/restore FPU/SSE
from xsave_area. So FPU/SSE states are incorrect after guest save/restore.

Ignoring AVX, that needs fixing in 4.0 branch. The state needs pulling out
of the xsave area and into the existing hvm_hw_cpu structure. Or, we disable
xsave by default on 4.0.x branch. What do you think?

I prefer to disable it by default on 4.0 branch now. After finish guest save/restore with XSAVE/XRSTOR in xen-unstable, we can port code to 4.0 branch and enable it again.

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