[vbox-dev] Virtualbox don't restore FPU segments with 32-bit guests while using xsave/xrstor

[quentin buathier]

Hi Michal,

I can't now give a way to reproduce the bug. I'll send an executable if I
manage to reproduce the problem on something minimalist.

But I can give you the context of the problem:
 Host OS: Debian jessie 64-bits


2016-05-12 11:52 GMT+02:00 Michal Necasek <michal.necasek at oracle.com>:

>
>    Hi Quentin,
>
>  Thank you for the patch!
>
>  Unfortunately (?) I can't reproduce the problem that was originally
> fixed. Could you please provide a bit more information? What's the host OS,
> guest OS, host CPU type? How to reproduce the problem?
>
>     Regards,
>       Michal
>
>
> On 5/12/2016 11:26 AM, quentin buathier wrote:
>
>> Hi,
>>
>> As I understand it, there used to be a problem with restoring the FPU
>> segments in case of a 64-bit hosts with a 32-bit guest. This issue has
>> been fixed by using the macros "SAVE_32_OR_64_FPU" and
>> "RESTORE_32_OR_64_FPU" in "src/VBox/VMM/VMMR0/CPUMR0A.asm" (when
>> Virtualbox was using fxsave and fxrstor to save and restore the FPU
>> context).
>>
>> But along with the recent support of xsave / xrstor, the bug was
>> reintroduced: if the CPU supports xsave/xrstor, Virtualbox uses these
>> instructions and the guest's FPU segments are not restored properly.
>>
>> Please find attached a possible patch to fix this issue (MIT licence).
>>
>> Regards,
>>
>>
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>>
>>
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