Re: [Xen-devel] Alignment check on domU (2.6.32)

[Natalie Protasevich <protasnb@xxxxxxxxx>]

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

>>> Natalie Protasevich <protasnb@xxxxxxxxx> 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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