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SubjectRe: mmu_notifier: close hole in fork
On Fri, 1 Feb 2008, Andrea Arcangeli wrote:

> Good catch! This was missing also in my #v5 (KVM doesn't need that
> because the only possible cows on sptes can be generated by ksm, but
> it would have been a problem for GRU). The more I think about it, the

How do you think the GRU should know when to drop the refcount? There is
no page table and thus no way of tracking that a refcount was taken.
Without the refcount you cannot defer the freeing of the page. So
shootdown on invalidate_range_begin and lock out until
invalidate_range_end seems to be the only workable solution.

BTW what do you think about adding a flag parameter to the invalidate
calls that allows shooting down writable ptes only? That could be useful
for COW and page_mkclean.

So

#define MMU_ATOMIC 1
#define MMU_WRITABLE 2

insted of the atomic parameter?





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