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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 14:20:05 +0100
- Cc: "Su, Disheng" <disheng.su@xxxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxx
- Delivery-date: Tue, 04 Dec 2007 05:41:00 -0800
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Wow... I had a mail in my drafts folder about exactly this. To answer the question if any OS's are affectedm, the answer is yes - OS/2 in newer versions than Warp 4 Fix Pack 12 gets stuck on this check. I've tested other guests with this check removed without any apparent ill effects, and was about to send a patch/RFC about removing it. It looks like 64 bit linux is the only guest that ever triggers the check, but like I said, I've seen no ill effect from removing the check even there.
On Dec 4, 2007 1:43 PM, Tim Deegan <
Tim.Deegan@xxxxxxxxxx> wrote: At 20:38 +0800 on 04 Dec (1196800681), Su, Disheng wrote:
> In in sh_x86_emulate_write:
> if ( vaddr & (bytes-1) )
> return X86EMUL_UNHANDLE;
> I met a problem the vaddr is not aligned on word or dword, but have to
> emulate it.
Have you got an OS that does unaligned writes to its pagetables?
Exciting! What is it doing?
> 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.
Tim.
--
Tim Deegan <Tim.Deegan@xxxxxxxxxx
>
Principal Software Engineer, Citrix Systems.
[Company #5334508: XenSource UK Ltd, reg'd c/o EC2Y 5EB, UK.]
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