Re: [PATCH 1/3] KVM: x86 emulator: Fix task switch privilege checks

[Kevin Wolf <kwolf@redhat.com>]

Am 27.01.2012 15:17, schrieb Joerg Roedel:
> On Fri, Jan 27, 2012 at 02:55:12PM +0100, Kevin Wolf wrote:
>> Am 27.01.2012 14:34, schrieb Joerg Roedel:
>>> On Fri, Jan 27, 2012 at 01:58:38PM +0100, Kevin Wolf wrote:
>>>> Am 25.01.2012 17:00, schrieb Joerg Roedel:
>>>
>>>> I just retried. I use kvm-kmod and kvm.git with HEAD at ff92e9b5 plus
>>>> the tree patches of this series plus a printk to output exit_int_info in
>>>> task_switch_intercept(). I ran taskswitch2 from kvm-unittests and got
>>>> two failures and my VM86 unit test which hung when trying to return from
>>>> VM86. I also ran the kernel that made me aware of the issue initially.
>>>> All debug messages show exit_int_info = 0.
>>>
>>> Okay, you are testing on a K8 which has exactly this bug. As I just
>>> found out it is documented as erratum 701. The good news is that this
>>> only happens on K8 and Fam11h, any later AMD processor doesn't have this
>>> bug.
>>
>> Meh. Unless you give me a newer processor, this doesn't really help
>> me... Doesn't look like there's any way to get a workaround, is there? I
>> guess I'll have to hack it locally and possibly break other guests with
>> the hacked module.
> 
> No, unfortunatly there is no workaround for this problem. How do you
> plan to hack around it?

I know that my guest only uses iret and exceptions for task switches, so
I think in my case I can assume that any TASK_SWITCH_CALL is really a
TASK_SWITCH_GATE and I don't have to skip an instruction.

Not quite upstreamable, obviously.

Kevin