Re: [PATCH 06/20] KVM: selftests: Read per-page value into local var when verifying dirty_log_test

Maxim Levitsky
2024-12-17T23:59:55Z

On Fri, 2024-12-13 at 17:07 -0800, Sean Christopherson wrote:
> Cache the page's value during verification in a local variable, re-reading
> from the pointer is ugly and error prone, e.g. allows for bugs like
> checking the pointer itself instead of the value.

You should note that there are no functional changes in this patch.

Besides this,

Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>

Best regards,
Maxim Levitsky

>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> ---
> tools/testing/selftests/kvm/dirty_log_test.c | 16 +++++++---------
> 1 file changed, 7 insertions(+), 9 deletions(-)
>
> diff --git a/tools/testing/selftests/kvm/dirty_log_test.c b/tools/testing/selftests/kvm/dirty_log_test.c
> index 08cbecd1a135..5a04a7bd73e0 100644
> --- a/tools/testing/selftests/kvm/dirty_log_test.c
> +++ b/tools/testing/selftests/kvm/dirty_log_test.c
> @@ -520,11 +520,10 @@ static void vm_dirty_log_verify(enum vm_guest_mode mode, unsigned long *bmap)
> {
> uint64_t page, nr_dirty_pages = 0, nr_clean_pages = 0;
> uint64_t step = vm_num_host_pages(mode, 1);
> - uint64_t *value_ptr;
> uint64_t min_iter = 0;
>
> for (page = 0; page < host_num_pages; page += step) {
> - value_ptr = host_test_mem + page * host_page_size;
> + uint64_t val = *(uint64_t *)(host_test_mem + page * host_page_size);
>
> /* If this is a special page that we were tracking... */
> if (__test_and_clear_bit_le(page, host_bmap_track)) {
> @@ -545,11 +544,10 @@ static void vm_dirty_log_verify(enum vm_guest_mode mode, unsigned long *bmap)
> * the corresponding page should be either the
> * previous iteration number or the current one.
> */
> - matched = (*value_ptr == iteration ||
> - *value_ptr == iteration - 1);
> + matched = (val == iteration || val == iteration - 1);
>
> if (host_log_mode == LOG_MODE_DIRTY_RING && !matched) {
> - if (*value_ptr == iteration - 2 && min_iter <= iteration - 2) {
> + if (val == iteration - 2 && min_iter <= iteration - 2) {
> /*
> * Short answer: this case is special
> * only for dirty ring test where the
> @@ -597,7 +595,7 @@ static void vm_dirty_log_verify(enum vm_guest_mode mode, unsigned long *bmap)
> TEST_ASSERT(matched,
> "Set page %"PRIu64" value %"PRIu64
> " incorrect (iteration=%"PRIu64")",
> - page, *value_ptr, iteration);
> + page, val, iteration);
> } else {
> nr_clean_pages++;
> /*
> @@ -619,11 +617,11 @@ static void vm_dirty_log_verify(enum vm_guest_mode mode, unsigned long *bmap)
> * we'll see that page P is cleared, with
> * value "iteration-1".
> */
> - TEST_ASSERT(*value_ptr <= iteration,
> + TEST_ASSERT(val <= iteration,
> "Clear page %"PRIu64" value %"PRIu64
> " incorrect (iteration=%"PRIu64")",
> - page, *value_ptr, iteration);
> - if (*value_ptr == iteration) {
> + page, val, iteration);
> + if (val == iteration) {
> /*
> * This page is _just_ modified; it
> * should report its dirtyness in the