[PATCH] mm/hmm: Prevent infinite loop in hmm_range_fault during EBUSY retries

[sooraj <sooraj20636@gmail.com>]

When hmm_vma_walk_test() skips a VMA (e.g., unsupported VM_IO/PFNMAP range),
it must update hmm_vma_walk->last to the end of the skipped VMA. Failing to
do so causes hmm_range_fault() to restart from the same address during
-EBUSY retries, reprocessing the skipped VMA indefinitely. This results in
an infinite loop if the VMA remains non-processable.

Update hmm_vma_walk->last to the VMA's end address in hmm_vma_walk_test()
when skipping the range. This ensures subsequent iterations resume correctly
after the skipped VMA, preventing infinite retry loops.

Signed-off-by: sooraj <sooraj20636@gmail.com>
---
 mm/hmm.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/mm/hmm.c b/mm/hmm.c
index 7e0229ae4a5a..29e3678fede5 100644
--- a/mm/hmm.c
+++ b/mm/hmm.c
@@ -547,6 +547,8 @@ static int hmm_vma_walk_test(unsigned long start, unsigned long end,
 
 	hmm_pfns_fill(start, end, range, HMM_PFN_ERROR);
 
+	/* Update last to the end of the skipped VMA to prevent reprocessing */
+	hmm_vma_walk->last = end;
 	/* Skip this vma and continue processing the next vma. */
 	return 1;
 }
-- 
2.45.2