[PATCH] mm/hmm/test: destroy xa_array instead of looping

[Ralph Campbell <rcampbell@nvidia.com>]

The test driver uses an xa_array to store virtual to physical address
translations for a simulated hardware device. The MMU notifier
invalidation callback is used to keep the table consistent with the CPU
page table and is frequently called only for a page or two. However, if
the test process exits unexpectedly or is killed, the range can be
[0..ULONG_MAX] in which case calling xa_erase() for every possible PFN
results in CPU timeouts. Munmap() can result in a large range being
invalidated but in that case, the xa_array is likely to contain entries
that need to be invalidated.
Check for [0..ULONG_MAX] explicitly and just destroy the whole table.

Signed-off-by: Ralph Campbell <rcampbell@nvidia.com>
---

This patch is based on Jason Gunthorpe's hmm tree and should be folded
into the ("mm/hmm/test: add selftest driver for HMM") patch once this
patch is reviewed, etc.

 lib/test_hmm.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/lib/test_hmm.c b/lib/test_hmm.c
index 8b36c26b717b..b89852ec3c29 100644
--- a/lib/test_hmm.c
+++ b/lib/test_hmm.c
@@ -201,7 +201,13 @@ static void dmirror_do_update(struct dmirror *dmirror, unsigned long start,
 	 * The XArray doesn't hold references to pages since it relies on
 	 * the mmu notifier to clear page pointers when they become stale.
 	 * Therefore, it is OK to just clear the entry.
+	 * However, if the entire address space is being invalidated, it
+	 * takes too long to clear them one at a time so destroy the array.
 	 */
+	if (start == 0 && end == ULONG_MAX) {
+		xa_destroy(&dmirror->pt);
+		return;
+	}
 	for (pfn = start >> PAGE_SHIFT; pfn < (end >> PAGE_SHIFT); pfn++)
 		xa_erase(&dmirror->pt, pfn);
 }
-- 
2.20.1