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

[Avi Kivity <avi@qumranet.com>]

Avi Kivity wrote:
> Joerg Rodel wrote:
>>> Meanwhile, I applied the patch, but I'm very worried about this.
>>>     
>>
>> Yes, we are also worried. Another question is why this only happens with
>> NPT. The SoftMMU code should also fail with shadow paging if there is a
>> bug.
>>   
>
> Slightly different paths -- direct_map vs page_fault.  Also, with npt, 
> all cpus will access the same pte that's being modified; without npt, 
> faults on the same page will result in different ptes being 
> instantiated, as each access will be from a different guest pte.
>
> Maybe we should turn on the dirty bit in the instantiated ptes -- that 
> will reduce the processor's mucking about with them.
>

I meant the accessed bit.  The dirty bit is always set, but the accessed 
bit it not, due to a bug.  Fixing it doesn't help, though.

-- 
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