Re: [PATCH 13/20] KVM: selftests: Print (previous) last_page on dirty page value mismatch

[Maxim Levitsky]

On Fri, 2024-12-13 at 17:07 -0800, Sean Christopherson wrote:
> Print out the last dirty pages from the current and previous iteration on
> verification failures.  In many cases, bugs (especially test bugs) occur
> on the edges, i.e. on or near the last pages, and being able to correlate
> failures with the last pages can aid in debug.
> 
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> ---
>  tools/testing/selftests/kvm/dirty_log_test.c | 13 ++++++++-----
>  1 file changed, 8 insertions(+), 5 deletions(-)
> 
> diff --git a/tools/testing/selftests/kvm/dirty_log_test.c b/tools/testing/selftests/kvm/dirty_log_test.c
> index d7cf1840bd80..fe8cc7f77e22 100644
> --- a/tools/testing/selftests/kvm/dirty_log_test.c
> +++ b/tools/testing/selftests/kvm/dirty_log_test.c
> @@ -566,8 +566,10 @@ static void vm_dirty_log_verify(enum vm_guest_mode mode, unsigned long *bmap)
>  				}
>  			}
>  
> -			TEST_FAIL("Dirty page %lu value (%lu) != iteration (%lu)",
> -				  page, val, iteration);
> +			TEST_FAIL("Dirty page %lu value (%lu) != iteration (%lu) "
> +				  "(last = %lu, prev_last = %lu)",
> +				  page, val, iteration, dirty_ring_last_page,
> +				  dirty_ring_prev_iteration_last_page);
>  		} else {
>  			nr_clean_pages++;
>  			/*
> @@ -590,9 +592,10 @@ static void vm_dirty_log_verify(enum vm_guest_mode mode, unsigned long *bmap)
>  			 *     value "iteration-1".
>  			 */
>  			TEST_ASSERT(val <= iteration,
> -				    "Clear page %"PRIu64" value %"PRIu64
> -				    " incorrect (iteration=%"PRIu64")",
> -				    page, val, iteration);
> +				    "Clear page %lu value (%lu) > iteration (%lu) "
> +				    "(last = %lu, prev_last = %lu)",
> +				    page, val, iteration, dirty_ring_last_page,
> +				    dirty_ring_prev_iteration_last_page);
>  			if (val == iteration) {
>  				/*
>  				 * This page is _just_ modified; it

Reviewed-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>