Re: [PATCH] KVM: SVM: fix random segfaults with NPT enabled

[Avi Kivity <avi@qumranet.com>]

Joerg Roedel wrote:
> On Wed, Aug 27, 2008 at 06:22:14PM +0300, Avi Kivity wrote:
>   
>> Joerg Rodel wrote:
>>     
>>> I will test it. Is the fix in your latest kernel.org tree? 
>>>       
>> It is now.  It doesn't fix the problem.
>>
>>     
>>> Reproduce it
>>> with a KVM guest and start tbench in it with around 100 clients
>>> configured. The tbench-process will crash when the bug is hit.
>>>  
>>>       
>> Does it reproduce with uniprocessor guests?
>>     
>
> Don't know yet. We will try that.
>
>   

It didn't reproduce here on uniprocessor, but I hadn't tried for long.

Some observations:

- tbench triggers many cases where we have concurrent faults on the same 
address.  these are serialized by mmu_lock.  I tried to have  
direct_map_entry() return is it detects a race.  didn't help.
- I instrumented set_shadow_pte() to warn if changing the pfn or 
writeable bit.  Didn't trip.

Are there any rules for touching npt ptes concurrently?

Meanwhile, I applied the patch, but I'm very worried about this.

-- 
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