Commits
Merge branch 'mmu_notifier_fixes'
Merge mmu_notifier fixes from Jérôme Glisse:
"The invalidate_page callback suffered from 2 pitfalls. First it used
to happen after page table lock was release and thus a new page might
have been setup for the virtual address before the call to
invalidate_page().
This is in a weird way fixed by commit c7ab0d2fdc84 ("mm: convert
try_to_unmap_one() to use page_vma_mapped_walk()") which moved the
callback under the page table lock. Which also broke several existing
user of the mmu_notifier API that assumed they could sleep inside this
callback.
The second pitfall was invalidate_page being the only callback not
taking a range of address in respect to invalidation but was giving an
address and a page. Lot of the callback implementer assumed this could
never be THP and thus failed to invalidate the appropriate range for
THP pages.
By killing this callback we unify the mmu_notifier callback API to
always take a virtual address range as input.
There is now two clear API (I am not mentioning the youngess API which
is seldomly used):
- invalidate_range_start()/end() callback (which allow you to sleep)
- invalidate_range() where you can not sleep but happen right after
page table update under page table lock
Note that a lot of existing user feels broken in respect to
range_start/ range_end. Many user only have range_start() callback but
there is nothing preventing them to undo what was invalidated in their
range_start() callback after it returns but before any CPU page table
update take place.
The code pattern use in kvm or umem odp is an example on how to
properly avoid such race. In a nutshell use some kind of sequence
number and active range invalidation counter to block anything that
might undo what the range_start() callback did.
If you do not care about keeping fully in sync with CPU page table (ie
you can live with CPU page table pointing to new different page for a
given virtual address) then you can take a reference on the pages
inside the range_start callback and drop it in range_end or when your
driver is done with those pages.
Last alternative is to use invalidate_range() if you can do
invalidation without sleeping as invalidate_range() callback happens
under the CPU page table spinlock right after the page table is
updated.
The first two patches convert existing mmu_notifier_invalidate_page()
calls to mmu_notifier_invalidate_range() and bracket those call with
call to mmu_notifier_invalidate_range_start()/end().
The next ten patches remove existing invalidate_page() callback as it
can no longer happen.
Finally the last page remove the invalidate_page() callback completely
so it can RIP.
Changes since v1:
- remove more dead code in kvm (no testing impact)
- more accurate end address computation (patch 2) in page_mkclean_one
and try_to_unmap_one
- added tested-by/reviewed-by gotten so far"
* emailed patches from Jérôme Glisse <jglisse@redhat.com>:
mm/mmu_notifier: kill invalidate_page
KVM: update to new mmu_notifier semantic v2
xen/gntdev: update to new mmu_notifier semantic
sgi-gru: update to new mmu_notifier semantic
misc/mic/scif: update to new mmu_notifier semantic
iommu/intel: update to new mmu_notifier semantic
iommu/amd: update to new mmu_notifier semantic
IB/hfi1: update to new mmu_notifier semantic
IB/umem: update to new mmu_notifier semantic
drm/amdgpu: update to new mmu_notifier semantic
powerpc/powernv: update to new mmu_notifier semantic
mm/rmap: update to new mmu_notifier semantic v2
dax: update to new mmu_notifier semantic
