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Re: [Xen-devel] Question about alignment check in sh_x86_emulate_write
- To: "Tim Deegan" <Tim.Deegan@xxxxxxxxxx>
- From: "Trolle Selander" <trolle.selander@xxxxxxxxx>
- Date: Tue, 4 Dec 2007 14:52:41 +0100
- Cc: "Su, Disheng" <disheng.su@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
- Delivery-date: Tue, 04 Dec 2007 05:53:34 -0800
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To expand on my hastily posted comment before - OS/2 does get snagged on the check because of unaligned page table writes.
On Dec 4, 2007 2:33 PM, Tim Deegan <
Tim.Deegan@xxxxxxxxxx> wrote: At 21:03 +0800 on 04 Dec (1196802182), Su, Disheng wrote:
> It does not write to pagetable. I am doing CR0.wp emulation(don't let
> guest turn off CR0.wp, but emulate the trapped instructions in shadow).
> Some applications like Anti-virus tools will turn off
CR0.wp to change
> guest IDT etc.
Oh, I see.
> >> I am wordering about the reason for this check. Is it safe to get
> >> rid of it?
> >
> > Not really. Among other things, self-aligned writes never cross page
> > boundaries.
> >
> Is it Ok to add the checking for cross page boundaries instead?
Yes, but you'll probably find you need page-crossing support as well if
you're emulating arbitrary memory writes. I believe we have a patch
somewhere that does that; I'll dig it out and polish it up for -unstable.
Cheers,
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