diff --git a/tools/testing/selftests/kvm/dirty_log_test.c b/tools/testing/selftests/kvm/dirty_log_test.c index aacf80f57439..cdae103314fc 100644 --- a/tools/testing/selftests/kvm/dirty_log_test.c +++ b/tools/testing/selftests/kvm/dirty_log_test.c @@ -152,6 +152,7 @@ static atomic_t vcpu_sync_stop_requested; * sem_vcpu_stop and before vcpu continues to run. */ static bool dirty_ring_vcpu_ring_full; + /* * This is only used for verifying the dirty pages. Dirty ring has a very * tricky case when the ring just got full, kvm will do userspace exit due to @@ -166,7 +167,51 @@ static bool dirty_ring_vcpu_ring_full; * dirty gfn we've collected, so that if a mismatch of data found later in the * verifying process, we let it pass. */ -static uint64_t dirty_ring_last_page; +static uint64_t dirty_ring_last_page = -1ULL; + +/* + * In addition to the above, it is possible (especially if this + * test is run nested) for the above scenario to repeat multiple times: + * + * The following can happen: + * + * - L1 vCPU: Memory write is logged to PML but not committed. + * + * - L1 test thread: Ignores the write because its last dirty ring entry + * Resets the dirty ring which: + * - Resets the A/D bits in EPT + * - Issues tlb flush (invept), which is intercepted by L0 + * + * - L0: frees the whole nested ept mmu root as the response to invept, + * and thus ensures that when memory write is retried, it will fault again + * + * - L1 vCPU: Same memory write is logged to the PML but not committed again. + * + * - L1 test thread: Ignores the write because its last dirty ring entry (again) + * Resets the dirty ring which: + * - Resets the A/D bits in EPT (again) + * - Issues tlb flush (again) which is intercepted by L0 + * + * ... + * + * N times + * + * - L1 vCPU: Memory write is logged in the PML and then committed. + * Lots of other memory writes are logged and committed. + * ... + * + * - L1 test thread: Sees the memory write along with other memory writes + * in the dirty ring, and since the write is usually not + * the last entry in the dirty-ring and has a very outdated + * iteration, the test fails. + * + * + * Note that this is only possible when the write was the last log entry + * write during iteration N-1, thus remember last iteration last log entry + * and also don't fail when it is reported in the next iteration, together with + * an outdated iteration count. + */ +static uint64_t dirty_ring_prev_iteration_last_page; enum log_mode_t { /* Only use KVM_GET_DIRTY_LOG for logging */ @@ -316,6 +361,8 @@ static uint32_t dirty_ring_collect_one(struct kvm_dirty_gfn *dirty_gfns, struct kvm_dirty_gfn *cur; uint32_t count = 0; + dirty_ring_prev_iteration_last_page = dirty_ring_last_page; + while (true) { cur = &dirty_gfns[*fetch_index % test_dirty_ring_count]; if (!dirty_gfn_is_dirtied(cur)) @@ -613,7 +660,8 @@ static void vm_dirty_log_verify(enum vm_guest_mode mode, unsigned long *bmap) */ min_iter = iteration - 1; continue; - } else if (page == dirty_ring_last_page) { + } else if (page == dirty_ring_last_page || + page == dirty_ring_prev_iteration_last_page) { /* * Please refer to comments in * dirty_ring_last_page.