Re: [PATCH 0/4] Swapping

[Avi Kivity <avi-atKUWr5tajBWk0Htik3J/w@public.gmane.org>]

Anthony Liguori wrote:
> I've been playing around with these patches.  If I do an 
> madvise(MADV_DONTNEED) in userspace, when I close the VM, I get the 
> following bug.  My knowledge of the mm is limited but since 
> madvise(MADV_DONTNEED) effectively does a zap_page_range() I wonder if 
> we're lacking the necessary callback to also remove any potential GPA 
> covered by that range from shadow page cache.
>
> Regards,
>
> Anthony Liguori
>
> [  860.724555] rmap_remove: ffff81004c48cf00 506d1025 0->BUG
>   

The mmu should keep a page's refcount elevated while it's mapped in, so
MADV_DONTNEED should not affect it.  Looks like there is a bug where kvm
looks at the host pagetables for a page which is already in the shadow
pagetables.  We need to avoid this as long as we don't have pte notifiers.

-- 
Do not meddle in the internals of kernels, for they are subtle and quick to panic.


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