Re: Alignment check on domU (2.6.32)

[Natalie Protasevich <protasnb@gmail.com>]

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On Tue, Mar 30, 2010 at 1:06 AM, Jan Beulich <JBeulich@novell.com> wrote:

> >>> Natalie Protasevich <protasnb@gmail.com> 30.03.10 05:08 >>>
> > I cheated and cleared the AM flag in cr0 (as one can see in this
> > trace) but this didn't help.
>
> Assuming you did this in the hypervisor, this would point at a CPU bug.
> There should not be any alignment check exceptions with this bit clear.
>
> > I haven't figured out what sets the AM flag...
>
> The hypervisor sets up CR0 this way, and doesn't allow altering later.
> In order to allow the kernel to support alignment check exceptions
> for user mode, Xen needs to do it this way and clears AC each time
> passing control to (64-bit) kernel code.
>

I was trying to be careful with AC/AM, but still messed up :) I meant to say
I can't find so far who sets the AC flag,  although I sprinkled checks in
various places, next was going to see how I can set HW breakpoint.


>
> What you'll need to do is look for where AC gets set, probably by
> modifying all asm-s using popf, as this is what seems bogus.
>

Thanks for the hint! I will look at those...

--Natalie

>
> Jan
>
>

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