Re: [PATCH] mmu notifiers #v2

Benjamin Herrenschmidt
2008-01-15T04:28:27Z

On Mon, 2008-01-14 at 12:02 -0800, Christoph Lameter wrote:
> On Sun, 13 Jan 2008, Andrea Arcangeli wrote:
>
> > About the locking perhaps I'm underestimating it, but by following the
> > TLB flushing analogy, by simply clearing the shadow ptes (with kvm
> > mmu_lock spinlock to avoid racing with other vcpu spte accesses of
> > course) and flushing the shadow-pte after clearing the main linux pte,
> > it should be enough to serialize against shadow-pte page faults that
> > would call into get_user_pages. Flushing the host TLB before or after
> > the shadow-ptes shouldn't matter.
>
> Hmmm... In most of the callsites we hold a writelock on mmap_sem right?

Not in unmap_mapping_range() afaik.

> > Comments welcome... especially from SGI/IBM/Quadrics and all other
> > potential users of this functionality.
>
> > There are also certain details I'm uncertain about, like passing 'mm'
> > to the lowlevel methods, my KVM usage of the invalidate_page()
> > notifier for example only uses 'mm' for a BUG_ON for example:
>
> Passing mm is fine as long as mmap_sem is held.

Passing mm is always a good idea, regardless of the mmap_sem, it can be
useful for lots of other things :-)

> > diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
> > --- a/include/asm-generic/pgtable.h
> > +++ b/include/asm-generic/pgtable.h
> > @@ -86,6 +86,7 @@ do { \
> > pte_t __pte; \
> > __pte = ptep_get_and_clear((__vma)->vm_mm, __address, __ptep); \
> > flush_tlb_page(__vma, __address); \
> > + mmu_notifier(invalidate_page, (__vma)->vm_mm, __address); \
> > __pte; \
> > })
> > #endif
>
> Hmmm... this is ptep_clear_flush? What about the other uses of
> flush_tlb_page in asm-generic/pgtable.h and related uses in arch code?
> (would help if your patches would mention the function name in the diff
> headers)

Note that last I looked, a lot of these were stale. Might be time to
resume my spring/summer cleaning of page table accessors...

> > +#define mmu_notifier(function, mm, args...) \
> > + do { \
> > + struct mmu_notifier *__mn; \
> > + struct hlist_node *__n; \
> > + \
> > + hlist_for_each_entry(__mn, __n, &(mm)->mmu_notifier, hlist) \
> > + if (__mn->ops->function) \
> > + __mn->ops->function(__mn, mm, args); \
> > + } while (0)
>
> Does this have to be inline? ptep_clear_flush will become quite big
>
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