6.1-stable review patch. If anyone has any objections, please let me know.
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From: Sean Christopherson seanjc@google.com
[ Upstream commit ba58f873cdeec30b6da48e28dd5782c5a3e1371b ]
When finishing the final iteration of dirty_log_test testcase, set host_quit _before_ the final "continue" so that the vCPU worker doesn't run an extra iteration, and delete the hack-a-fix of an extra "continue" from the dirty ring testcase. This fixes a bug where the extra post to sem_vcpu_cont may not be consumed, which results in failures in subsequent runs of the testcases. The bug likely was missed during development as x86 supports only a single "guest mode", i.e. there aren't any subsequent testcases after the dirty ring test, because for_each_guest_mode() only runs a single iteration.
For the regular dirty log testcases, letting the vCPU run one extra iteration is a non-issue as the vCPU worker waits on sem_vcpu_cont if and only if the worker is explicitly told to stop (vcpu_sync_stop_requested). But for the dirty ring test, which needs to periodically stop the vCPU to reap the dirty ring, letting the vCPU resume the guest _after_ the last iteration means the vCPU will get stuck without an extra "continue".
However, blindly firing off an post to sem_vcpu_cont isn't guaranteed to be consumed, e.g. if the vCPU worker sees host_quit==true before resuming the guest. This results in a dangling sem_vcpu_cont, which leads to subsequent iterations getting out of sync, as the vCPU worker will continue on before the main task is ready for it to resume the guest, leading to a variety of asserts, e.g.
==== Test Assertion Failure ==== dirty_log_test.c:384: dirty_ring_vcpu_ring_full pid=14854 tid=14854 errno=22 - Invalid argument 1 0x00000000004033eb: dirty_ring_collect_dirty_pages at dirty_log_test.c:384 2 0x0000000000402d27: log_mode_collect_dirty_pages at dirty_log_test.c:505 3 (inlined by) run_test at dirty_log_test.c:802 4 0x0000000000403dc7: for_each_guest_mode at guest_modes.c:100 5 0x0000000000401dff: main at dirty_log_test.c:941 (discriminator 3) 6 0x0000ffff9be173c7: ?? ??:0 7 0x0000ffff9be1749f: ?? ??:0 8 0x000000000040206f: _start at ??:? Didn't continue vcpu even without ring full
Alternatively, the test could simply reset the semaphores before each testcase, but papering over hacks with more hacks usually ends in tears.
Reported-by: Shaoqin Huang shahuang@redhat.com Fixes: 84292e565951 ("KVM: selftests: Add dirty ring buffer test") Reviewed-by: Peter Xu peterx@redhat.com Reviewed-by: Shaoqin Huang shahuang@redhat.com Link: https://lore.kernel.org/r/20240202231831.354848-1-seanjc@google.com Signed-off-by: Sean Christopherson seanjc@google.com Signed-off-by: Sasha Levin sashal@kernel.org --- tools/testing/selftests/kvm/dirty_log_test.c | 50 +++++++++++--------- 1 file changed, 27 insertions(+), 23 deletions(-)
diff --git a/tools/testing/selftests/kvm/dirty_log_test.c b/tools/testing/selftests/kvm/dirty_log_test.c index 8758c10ec850..ec40a33c29fd 100644 --- a/tools/testing/selftests/kvm/dirty_log_test.c +++ b/tools/testing/selftests/kvm/dirty_log_test.c @@ -355,7 +355,10 @@ static void dirty_ring_collect_dirty_pages(struct kvm_vcpu *vcpu, int slot,
cleared = kvm_vm_reset_dirty_ring(vcpu->vm);
- /* Cleared pages should be the same as collected */ + /* + * Cleared pages should be the same as collected, as KVM is supposed to + * clear only the entries that have been harvested. + */ TEST_ASSERT(cleared == count, "Reset dirty pages (%u) mismatch " "with collected (%u)", cleared, count);
@@ -394,12 +397,6 @@ static void dirty_ring_after_vcpu_run(struct kvm_vcpu *vcpu, int ret, int err) } }
-static void dirty_ring_before_vcpu_join(void) -{ - /* Kick another round of vcpu just to make sure it will quit */ - sem_post(&sem_vcpu_cont); -} - struct log_mode { const char *name; /* Return true if this mode is supported, otherwise false */ @@ -412,7 +409,6 @@ struct log_mode { uint32_t *ring_buf_idx); /* Hook to call when after each vcpu run */ void (*after_vcpu_run)(struct kvm_vcpu *vcpu, int ret, int err); - void (*before_vcpu_join) (void); } log_modes[LOG_MODE_NUM] = { { .name = "dirty-log", @@ -431,7 +427,6 @@ struct log_mode { .supported = dirty_ring_supported, .create_vm_done = dirty_ring_create_vm_done, .collect_dirty_pages = dirty_ring_collect_dirty_pages, - .before_vcpu_join = dirty_ring_before_vcpu_join, .after_vcpu_run = dirty_ring_after_vcpu_run, }, }; @@ -492,14 +487,6 @@ static void log_mode_after_vcpu_run(struct kvm_vcpu *vcpu, int ret, int err) mode->after_vcpu_run(vcpu, ret, err); }
-static void log_mode_before_vcpu_join(void) -{ - struct log_mode *mode = &log_modes[host_log_mode]; - - if (mode->before_vcpu_join) - mode->before_vcpu_join(); -} - static void generate_random_array(uint64_t *guest_array, uint64_t size) { uint64_t i; @@ -701,6 +688,7 @@ static void run_test(enum vm_guest_mode mode, void *arg) struct kvm_vm *vm; unsigned long *bmap; uint32_t ring_buf_idx = 0; + int sem_val;
if (!log_mode_supported()) { print_skip("Log mode '%s' not supported", @@ -772,12 +760,22 @@ static void run_test(enum vm_guest_mode mode, void *arg) /* Start the iterations */ iteration = 1; sync_global_to_guest(vm, iteration); - host_quit = false; + WRITE_ONCE(host_quit, false); host_dirty_count = 0; host_clear_count = 0; host_track_next_count = 0; WRITE_ONCE(dirty_ring_vcpu_ring_full, false);
+ /* + * Ensure the previous iteration didn't leave a dangling semaphore, i.e. + * that the main task and vCPU worker were synchronized and completed + * verification of all iterations. + */ + sem_getvalue(&sem_vcpu_stop, &sem_val); + TEST_ASSERT_EQ(sem_val, 0); + sem_getvalue(&sem_vcpu_cont, &sem_val); + TEST_ASSERT_EQ(sem_val, 0); + pthread_create(&vcpu_thread, NULL, vcpu_worker, vcpu);
while (iteration < p->iterations) { @@ -803,15 +801,21 @@ static void run_test(enum vm_guest_mode mode, void *arg) assert(host_log_mode == LOG_MODE_DIRTY_RING || atomic_read(&vcpu_sync_stop_requested) == false); vm_dirty_log_verify(mode, bmap); - sem_post(&sem_vcpu_cont);
- iteration++; + /* + * Set host_quit before sem_vcpu_cont in the final iteration to + * ensure that the vCPU worker doesn't resume the guest. As + * above, the dirty ring test may stop and wait even when not + * explicitly request to do so, i.e. would hang waiting for a + * "continue" if it's allowed to resume the guest. + */ + if (++iteration == p->iterations) + WRITE_ONCE(host_quit, true); + + sem_post(&sem_vcpu_cont); sync_global_to_guest(vm, iteration); }
- /* Tell the vcpu thread to quit */ - host_quit = true; - log_mode_before_vcpu_join(); pthread_join(vcpu_thread, NULL);
pr_info("Total bits checked: dirty (%"PRIu64"), clear (%"PRIu64"), "