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[Xen-devel] Re: Should shadow_fault_fast_fail abort?

from [Tim Deegan]

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To:	Herbert Xu <herbert@xxxxxxxxxxxxxxxxxxx>
Subject:	[Xen-devel] Re: Should shadow_fault_fast_fail abort?
From:	Tim Deegan <Tim.Deegan@xxxxxxxxxxxxx>
Date:	Fri, 15 Dec 2006 09:27:45 +0000
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At 15:42 +1100 on 15 Dec (1166197339), Herbert Xu wrote:
> I noticed your recent patch turned off PFEC_reserved_bit in case
> another CPU had already modified a magic PTE.  It seems that it
> still leaves PFEC_page_present enabled.  This could confuse the
> guest if the PTE modification is such that the PTE is now present
> and valid.  In fact the guest may treat it as a protection fault.

It's just a spurious page fault -- the hardware is happy to throw these
at operating systems and so am I. :)  

> The safest solution is probably to just return EXCRET_fault_fixed
> and let the CPU figure it out.

That does seem cleaner.  Is this a problem you were seeing on a
particular system, or just a general improvement?

Cheers,

Tim.

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