[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 but 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
 Guest OS: Debian jessie 32-bits
 Processor: i7-2600 (and all i7 tested)

PS: Sorry for the previous mail that was accidently sent

Regards,

2016-05-12 12:18 GMT+02:00 quentin buathier <qbuathier at tetrane.com>:

> 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,
>>>
>>>
>>> _______________________________________________
>>> vbox-dev mailing list
>>> vbox-dev at virtualbox.org
>>> https://www.virtualbox.org/mailman/listinfo/vbox-dev
>>>
>>>
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>
>
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