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Subject[PATCH 3/4] mm/hmm: allow hmm_range_fault() of mmap(PROT_NONE)
Date
Allow hmm_range_fault() to return success (0) when the range has no access
(!(vma->vm_flags & VM_READ)). The range->pfns[] array will be filled with
range->values[HMM_PFN_NONE] in this case.
This allows the caller to get a snapshot of a range without having to
lookup the vma before calling hmm_range_fault().
If the call to hmm_range_fault() is not a snapshot, the caller can still
check that pfns have the desired access permissions.

Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
Cc: "Jérôme Glisse" <jglisse@redhat.com>
Cc: Jason Gunthorpe <jgg@mellanox.com>
Cc: Christoph Hellwig <hch@lst.de>
---
mm/hmm.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/mm/hmm.c b/mm/hmm.c
index 7217912bef13..16c834e5d1c0 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -795,7 +795,9 @@ static int hmm_vma_walk_test(unsigned long start,
*/
if (!(vma->vm_flags & VM_READ)) {
(void) hmm_pfns_fill(start, end, range, HMM_PFN_NONE);
- return -EPERM;
+
+ /* Skip this vma and continue processing the next vma. */
+ return 1;
}

return 0;
--
2.20.1
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