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

To: "Natalie Protasevich" <protasnb@xxxxxxxxx>
Subject: Re: [Xen-devel] Alignment check on domU (2.6.32)
From: "Jan Beulich" <JBeulich@xxxxxxxxxx>
Date: Tue, 30 Mar 2010 09:06:12 +0100
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>>> 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.

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.


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