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Re: [Xen-devel] [PATCH][SVM][1/2] fix SVM 64bit hv cores>0 reboot/hang i

To: "Woller, Thomas" <thomas.woller@xxxxxxx>
Subject: Re: [Xen-devel] [PATCH][SVM][1/2] fix SVM 64bit hv cores>0 reboot/hang issue
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Thu, 4 May 2006 11:10:00 +0100
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On 3 May 2006, at 22:17, Woller, Thomas wrote:

Now, cursory testing on VT boxes indicates that the 0x2B selectors are
also restored on VMX, but the VT microcode does not seem to validate
these values, and therefore does not cause a processor shutdown.

These registers are officially ignored in 64bit mode, and zero'ing them
out seems to be a solution that is functional, but we're unsure as to
the use of the __USER_DS 0x2B values in ds, es selectors in 64bit mode.

Zeroing them out is probably the best thing to do. Xen doesn't bother to change them while it executes because ds/es/ss are effectively unused in 64-bit mode. The fact they happen to contain __USER_DS is utterly unimportant.

You probably need to worry about fs and gs as well. They're not causing you problems now because guests don't usually set those registers to non-zero values, but if they ever do then you'll presumably have problems?

So, I think the patch is good but needs to zero fs/gs as well. I'll wait for further advice before applying this patch.

 -- Keir

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