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KVM: selftests: Keep dirty_log_test vCPU in guest until it needs to stop

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In the dirty_log_test guest code, exit to userspace only when the vCPU is
explicitly told to stop.  Periodically exiting just to check if a flag has
been set is unnecessary, weirdly complex, and wastes time handling exits
that could be used to dirty memory.

Opportunistically convert 'i' to a uint64_t to guard against the unlikely
scenario that guest_num_pages exceeds the storage of an int.

Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Link: https://lore.kernel.org/r/20250111003004.1235645-11-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson 2025-01-10 16:29:54 -08:00
parent f3629c0ef1
commit 0a818b3541
1 changed files with 22 additions and 21 deletions
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43
tools/testing/selftests/kvm/dirty_log_test.c
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@ -31,9 +31,6 @@
/* Default guest test virtual memory offset */
#define DEFAULT_GUEST_TEST_MEM 0xc0000000
/* How many pages to dirty for each guest loop */
#define TEST_PAGES_PER_LOOP 1024
/* How many host loops to run (one KVM_GET_DIRTY_LOG for each loop) */
#define TEST_HOST_LOOP_N 32UL
@ -75,6 +72,7 @@ static uint64_t host_page_size;
static uint64_t guest_page_size;
static uint64_t guest_num_pages;
static uint64_t iteration;
static bool vcpu_stop;
/*
* Guest physical memory offset of the testing memory slot.
@ -96,9 +94,10 @@ static uint64_t guest_test_virt_mem = DEFAULT_GUEST_TEST_MEM;
static void guest_code(void)
{
uint64_t addr;
int i;
#ifdef __s390x__
uint64_t i;
/*
* On s390x, all pages of a 1M segment are initially marked as dirty
* when a page of the segment is written to for the very first time.
@ -112,7 +111,7 @@ static void guest_code(void)
#endif
while (true) {
for (i = 0; i < TEST_PAGES_PER_LOOP; i++) {
while (!READ_ONCE(vcpu_stop)) {
addr = guest_test_virt_mem;
addr += (guest_random_u64(&guest_rng) % guest_num_pages)
* guest_page_size;
@ -140,14 +139,7 @@ static uint64_t host_track_next_count;
/* Whether dirty ring reset is requested, or finished */
static sem_t sem_vcpu_stop;
static sem_t sem_vcpu_cont;
/*
* This is only set by main thread, and only cleared by vcpu thread. It is
* used to request vcpu thread to stop at the next GUEST_SYNC, since GUEST_SYNC
* is the only place that we'll guarantee both "dirty bit" and "dirty data"
* will match. E.g., SIG_IPI won't guarantee that if the vcpu is interrupted
* after setting dirty bit but before the data is written.
*/
static atomic_t vcpu_sync_stop_requested;
/*
* This is updated by the vcpu thread to tell the host whether it's a
* ring-full event. It should only be read until a sem_wait() of
@ -272,9 +264,7 @@ static void clear_log_collect_dirty_pages(struct kvm_vcpu *vcpu, int slot,
/* Should only be called after a GUEST_SYNC */
static void vcpu_handle_sync_stop(void)
{
if (atomic_read(&vcpu_sync_stop_requested)) {
/* It means main thread is sleeping waiting */
atomic_set(&vcpu_sync_stop_requested, false);
if (READ_ONCE(vcpu_stop)) {
sem_post(&sem_vcpu_stop);
sem_wait(&sem_vcpu_cont);
}
@ -801,11 +791,24 @@ static void run_test(enum vm_guest_mode mode, void *arg)
}
/*
* See vcpu_sync_stop_requested definition for details on why
* we need to stop vcpu when verify data.
* Stop the vCPU prior to collecting and verifying the dirty
* log. If the vCPU is allowed to run during collection, then
* pages that are written during this iteration may be missed,
* i.e. collected in the next iteration. And if the vCPU is
* writing memory during verification, pages that this thread
* sees as clean may be written with this iteration's value.
*/
atomic_set(&vcpu_sync_stop_requested, true);
WRITE_ONCE(vcpu_stop, true);
sync_global_to_guest(vm, vcpu_stop);
sem_wait(&sem_vcpu_stop);
/*
* Clear vcpu_stop after the vCPU thread has acknowledge the
* stop request and is waiting, i.e. is definitely not running!
*/
WRITE_ONCE(vcpu_stop, false);
sync_global_to_guest(vm, vcpu_stop);
/*
* NOTE: for dirty ring, it's possible that we didn't stop at
* GUEST_SYNC but instead we stopped because ring is full;
@ -813,8 +816,6 @@ static void run_test(enum vm_guest_mode mode, void *arg)
* the flush of the last page, and since we handle the last
* page specially verification will succeed anyway.
*/
assert(host_log_mode == LOG_MODE_DIRTY_RING ||
atomic_read(&vcpu_sync_stop_requested) == false);
vm_dirty_log_verify(mode, bmap);
/*