Re: [Xen-devel] [PATCH] Add xsave/xrstor support to Xen

To:	"Cui, Dexuan" <dexuan.cui@xxxxxxxxx>, <xen-devel@xxxxxxxxxxxxxxxxxxx>
Subject:	Re: [Xen-devel] [PATCH] Add xsave/xrstor support to Xen
From:	Keir Fraser <keir.fraser@xxxxxxxxxxxxx>
Date:	Wed, 28 May 2008 14:37:32 +0100
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On 28/5/08 14:11, "Cui, Dexuan" <dexuan.cui@xxxxxxxxx> wrote:

> For now, the xsave_area is at least 512 + 64 (the xsave header) = 576 bytes in
> length, though the first 512 bytes are completely compatible with the legacy
> 512-byte arch.guest_context.fpu_ctxt; actually we also have to save the
> per-vcpu 64-bit "xfeature_mask", and the gloabal variables
> "xsave_cntxt_max_size, xfeature_low, xfeature_high" (imagine different CPU has
> different XSAVE capability). So I think we have to extend  the current
> save/restore format.

I must say I am happy to wait until there are some actual extended state
vectors to be saved. It's not clear that the XSAVE format is the right way
to extend the HVM save/restore format. The right direction may depend on
what types of new state are introduced, whether these are achitectural or
vendor-specific, etc. It doesn't sound like there's a downside to sitting on
the fence and doing nothing for now.

 -- Keir

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