Re: [Xen-devel] Question about alignment check in sh_x86_emulate_write

["Trolle Selander" <trolle.selander@xxxxxxxxx>]

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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