Re: [PATCH] x86_64,xen,espfix: Initialize espfix on secondary CPUs

[Andy Lutomirski]

On Tue, Jul 15, 2014 at 9:05 AM, Boris Ostrovsky
<boris.ostrovsky@xxxxxxxxxx> wrote:
> On 07/15/2014 11:54 AM, Andy Lutomirski wrote:
>>
>> On Tue, Jul 15, 2014 at 8:45 AM, Boris Ostrovsky
>> <boris.ostrovsky@xxxxxxxxxx> wrote:
>>>
>>> On 07/15/2014 11:38 AM, Konrad Rzeszutek Wilk wrote:
>>>>
>>>> On Tue, Jul 15, 2014 at 08:26:41AM -0700, Andy Lutomirski wrote:
>>>>>
>>>>> Xen doesn't call start_secondary.
>>>>
>>>> Duh!
>>>>>
>>>>> Cc: stable@xxxxxxxxxxxxxxx
>>>>> Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
>>>>> ---
>>>>>
>>>>> espfix still doesn't seem to work on Xen (it goes boom in some way that
>>>>> I don't understand right now), but initializing all CPUs instead of
>>>>> just
>>>>> one of them seems like a good start.
>>>>>
>>>>> ISTM the right fix is probably to shove the espfix logic into
>>>>> native_iret and to tweak the paravirt logic so that native_iret always
>>>>> gets invoked.  I suspect that Xen will need its own implementation of
>>>>> espfix64 in the hypervisor and that, ultimately, someone may want to
>>>>> stop initializing espfix64 at all on Xen guests.
>>>>
>>>> I think just disallowing would be preferrable.
>>>
>>>
>>> I've been looking at sigreturn_64 and it seems to be crashing dom0 (with
>>> both mine and your patches). In kprobe_int3_handler().
>>
>> You need:
>>
>>
>> http://lkml.kernel.org/g/c4e339882c121aa76254f2adde3fcbdf502faec2.1405099506.git.luto@xxxxxxxxxxxxxx
>>
>> The newer version of sigreturn_32 that I pushed is a much better test
>> -- it tests the 64-bit cases (yay thunks!) and works on kernels
>> without my SS sigcontext fix.
>
>
> Yes, that does it. At least we don't have yet another failure mode with
> this, which was the biggest concern.

I updated the sigreturn test again -- the new version exercises the
double-fault case, too.  It passes on a non-Xen kernel with the
krpobes fix.

--Andy

>
> Thanks.
>
> -boris
>



-- 
Andy Lutomirski
AMA Capital Management, LLC
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