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

Avi Kivity
2008-08-27T15:21:42Z

Joerg Rodel wrote:

>> hm. tbench doesn't allocate memory, so there shouldn't be any npt faults. I don't
>> see how this can make a difference.
>>
>
>

I reproduced it. There are a few npt faults as the guest has not
touched all of memory yet. If I force it to touch all of memory (dd <
/dev/hda), the problem appears to go away.

> Base for the fix was this bugreport:
>
> http://sourceforge.net/tracker/index.php?func=detail&aid=2019053&group_id=180599&atid=893831
>
> We found out that the same crash occur on long running compile
> workloads and that stale tlb-entries cause it. Until we find the real
> location of the missing tlb flush in the mmu code, i think its best to
> flush the TLB every time the mapping/unmapping code for the nested page
> table is executed. This fixes at least the crashes in the guest and has
> only minimal performance impact.
>

I'd like to try and find out what the problem is exactly. Otherwise we
may be only narrowing the window, not closing it.

--
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