Re: Debugging an inconsistent shadow page table

[Jan Kiszka <jan.kiszka@web.de>]

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Gleb Natapov wrote:
> On Sun, Apr 26, 2009 at 01:36:22PM +0200, Jan Kiszka wrote:
>> Gleb Natapov wrote:
>>> On Sun, Apr 26, 2009 at 01:11:40PM +0200, Jan Kiszka wrote:
>>>> That raise a question for a kvm-mmu newbie like me:
>>>>
>>>> If a page of the qemu process gets pushed around (here likely due to
>>>> fork()->exec(smbd)->COW), how will kvm's shadow table catch up? Via
>>>> MMU_NOTIFIER?
>>>>
>>>> I'm on a 2.6.25 kernel, and that means without CONFIG_MMU_NOTIFIER. So
>>>> far I assumed that kernels without this feature do not work optimally,
>>>> but they won't break my guests...
>>>>
>>> Guest memory is not COWed on fork (madvise(MADV_DONTFORK))
>> Yeah... but that's missing upstream! Will cross-check and then post a
>> fix for qemu.
>>
>> Out of curiosity: What's the mechanism to update the shadow table after
>> swap-out/swap-in?
>>
> I don't think guest memory is swappable without mmu notifiers. 

Given the experience with COW: How is this ensured, or where is this
done upstream?

Jan


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