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

[Tim Deegan <Tim.Deegan@xxxxxxxxxx>]

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,

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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