[PATCH v6 4/4] mshv: Use hmm_range_fault_unlocked() for region faults

[Stanislav Kinsburskii]

Convert mshv_region_hmm_fault_and_lock() to use
hmm_range_fault_unlocked() instead of taking mmap_read_lock() around
hmm_range_fault() directly.

This lets the HMM helper own the mmap read lock and allows the MSHV fault
path to handle mappings whose fault handlers may drop mmap_lock, including
userfaultfd-backed VMAs. The existing caller already retries on -EBUSY
after refreshing the mmu_interval_notifier sequence, so no control flow
change is needed beyond using the unlocked helper.

Signed-off-by: Stanislav Kinsburskii <skinsburskii@xxxxxxxxx>
---
 drivers/hv/mshv_regions.c |   14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

diff --git a/drivers/hv/mshv_regions.c b/drivers/hv/mshv_regions.c
index 6d65e5b42152..04676f06c5c7 100644
--- a/drivers/hv/mshv_regions.c
+++ b/drivers/hv/mshv_regions.c
@@ -388,13 +388,11 @@ int mshv_region_get(struct mshv_mem_region *region)
  *
  * This function performs the following steps:
  * 1. Reads the notifier sequence for the HMM range.
- * 2. Acquires a read lock on the memory map.
- * 3. Handles HMM faults for the specified range.
- * 4. Releases the read lock on the memory map.
- * 5. If successful, locks the memory region mutex.
- * 6. Verifies if the notifier sequence has changed during the operation.
+ * 2. Handles HMM faults for the specified range.
+ * 3. If successful, locks the memory region mutex.
+ * 4. Verifies if the notifier sequence has changed during the operation.
  *    If it has, releases the mutex and returns -EBUSY to match with
- *    hmm_range_fault() return code for repeating.
+ *    hmm_range_fault_unlocked() so the caller retries the range fault.
  *
  * Return: 0 on success, a negative error code otherwise.
  */
@@ -404,9 +402,7 @@ static int mshv_region_hmm_fault_and_lock(struct mshv_mem_region *region,
 	int ret;
 
 	range->notifier_seq = mmu_interval_read_begin(range->notifier);
-	mmap_read_lock(region->mreg_mni.mm);
-	ret = hmm_range_fault(range);
-	mmap_read_unlock(region->mreg_mni.mm);
+	ret = hmm_range_fault_unlocked(range);
 	if (ret)
 		return ret;