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Re: [Xen-devel] xm save + restore crashes Windows 200832-bit(4.0.2-rc2-p

To: James Harper <james.harper@xxxxxxxxxxxxxxxx>
Subject: Re: [Xen-devel] xm save + restore crashes Windows 200832-bit(4.0.2-rc2-pre) (AMD only)
From: Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Date: Tue, 25 Jan 2011 22:21:49 +0000
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At 22:11 +0000 on 25 Jan (1295993487), James Harper wrote:
> > 
> > At 13:35 +0000 on 25 Jan (1295962540), James Harper wrote:
> > > So the problem is somewhere past hvm_set_segment_register, and
> because
> > > it's amd only, probably in or beyond svm_set_segment_register. The
> first
> > > thing I notice in that routine is that there is a case for those 4
> > > registers... although all it seems to do is svm_sync_vmcb before and
> > > svm_vmload after setting. I don't know what those two do though.
> > 
> > Hmm; I suspect the bug here is actually in the save side -- the
> syncing
> > of the vmcb in the save routine is not conditional on v == current,
> and
> > the "already synced" bit that it would otherwise gate on isn't
> properly
> > initialized.
> > 
> > Try the attached patch; I'm sorry to say that I suspect it will fix
> the
> > odd output of xen_hvmctx but probably won't fix the BSOD. :(
> > 
> Just to clarify, in the restore path I print the values to be saved to
> the segment registers, then I read the segment registers and print the
> values that are in them. They aren't the same. Doesn't that sound like a
> problem on the restore side?

That would depend on how you read the values after the restore - the
patch is for a bug that I think is causing svm_get_segment_register() to
corrupt the vmcb if it's called before the vcpu is first scheduled (and
to return the corrupted values).



Tim Deegan <Tim.Deegan@xxxxxxxxxx>
Principal Software Engineer, Xen Platform Team
Citrix Systems UK Ltd.  (Company #02937203, SL9 0BG)

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