[PATCH 17/20] KVM: selftests: Tighten checks around prev iter's last dirty page in ring

Sean Christopherson
2024-12-14T01:07:53Z

Now that each iteration collects all dirty entries and ensures the guest
*completes* at least one write, tighten the exemptions for the last dirty
page of the previous iteration. Specifically, the only legal value (other
than the current iteration) is N-1.

Unlike the last page for the current iteration, the in-progress write from
the previous iteration is guaranteed to have completed, otherwise the test
would have hung.

Signed-off-by: Sean Christopherson <seanjc@google.com>
---
tools/testing/selftests/kvm/dirty_log_test.c | 22 +++++++++++++-------
1 file changed, 15 insertions(+), 7 deletions(-)

diff --git a/tools/testing/selftests/kvm/dirty_log_test.c b/tools/testing/selftests/kvm/dirty_log_test.c
index 8eb51597f762..18d41537e737 100644
--- a/tools/testing/selftests/kvm/dirty_log_test.c
+++ b/tools/testing/selftests/kvm/dirty_log_test.c
@@ -517,14 +517,22 @@ static void vm_dirty_log_verify(enum vm_guest_mode mode, unsigned long **bmap)

if (host_log_mode == LOG_MODE_DIRTY_RING) {
/*
- * The last page in the ring from this iteration
- * or the previous can be written with the value
- * from the previous iteration (relative to the
- * last page's iteration), as the value to be
- * written may be cached in a CPU register.
+ * The last page in the ring from previous
+ * iteration can be written with the value
+ * from the previous iteration, as the value to
+ * be written may be cached in a CPU register.
*/
- if ((page == dirty_ring_last_page ||
- page == dirty_ring_prev_iteration_last_page) &&
+ if (page == dirty_ring_prev_iteration_last_page &&
+ val == iteration - 1)
+ continue;
+
+ /*
+ * Any value from a previous iteration is legal
+ * for the last entry, as the write may not yet
+ * have retired, i.e. the page may hold whatever
+ * it had before this iteration started.
+ */
+ if (page == dirty_ring_last_page &&
val < iteration)
continue;
} else if (!val && iteration == 1 && bmap0_dirty) {
--
2.47.1.613.gc27f4b7a9f-goog