[PATCH v10 5/8] drm/nouveau: Use hmm_range_fault_unlocked_timeout() for SVM faults

[Stanislav Kinsburskii <skinsburskii@gmail.com>]

nouveau_range_fault() takes mmap_read_lock() only to call
hmm_range_fault(). It also keeps a single HMM_RANGE_DEFAULT_TIMEOUT
deadline across both HMM -EBUSY retries and post-fault
mmu_interval_read_retry() retries.

Use hmm_range_fault_unlocked_timeout() instead. The HMM helper now owns
the mmap lock and refreshes range->notifier_seq for its internal retries.
Nouveau keeps its existing absolute deadline in the outer loop and passes
the remaining jiffies to the helper for each fault attempt, so retries
caused by mmu_interval_read_retry() do not reset the overall retry budget.

Nouveau still validates the interval notifier sequence while holding
svmm->mutex before programming the GPU mapping.

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Signed-off-by: Stanislav Kinsburskii <skinsburskii@gmail.com>
---
 drivers/gpu/drm/nouveau/nouveau_svm.c | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/drivers/gpu/drm/nouveau/nouveau_svm.c b/drivers/gpu/drm/nouveau/nouveau_svm.c
index dcc92131488e..58735446d783 100644
--- a/drivers/gpu/drm/nouveau/nouveau_svm.c
+++ b/drivers/gpu/drm/nouveau/nouveau_svm.c
@@ -678,20 +678,22 @@ static int nouveau_range_fault(struct nouveau_svmm *svmm,
 	range.end = notifier->notifier.interval_tree.last + 1;
 
 	while (true) {
-		if (time_after(jiffies, timeout)) {
+		long remaining = timeout - jiffies;
+
+		/*
+		 * The HMM timeout only bounds retries while HMM is walking and
+		 * faulting the range. This fault is handled by a kernel worker,
+		 * so fatal signals from the faulting process cannot stop an
+		 * endless stream of invalidations here.
+		 */
+		if (time_after_eq(jiffies, timeout)) {
 			ret = -EBUSY;
 			goto out;
 		}
 
-		range.notifier_seq = mmu_interval_read_begin(range.notifier);
-		mmap_read_lock(mm);
-		ret = hmm_range_fault(&range);
-		mmap_read_unlock(mm);
-		if (ret) {
-			if (ret == -EBUSY)
-				continue;
+		ret = hmm_range_fault_unlocked_timeout(&range, remaining);
+		if (ret)
 			goto out;
-		}
 
 		mutex_lock(&svmm->mutex);
 		if (mmu_interval_read_retry(range.notifier,

-- 
2.43.0