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

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

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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