Re: [PATCH] KVM: selftests: Don't assert on exact number of 4KiB in dirty log split test

[Tao Su]

On Wed, Jan 31, 2024 at 02:27:28PM -0800, Sean Christopherson wrote:
> Drop dirty_log_page_splitting_test's assertion that the number of 4KiB
> pages remains the same across dirty logging being enabled and disabled, as
> the test doesn't guarantee that mappings outside of the memslots being
> dirty logged are stable, e.g. KVM's mappings for code and pages in
> memslot0 can be zapped by things like NUMA balancing.
> 
> To preserve the spirit of the check, assert that (a) the number of 4KiB
> pages after splitting is _at least_ the number of 4KiB pages across all
> memslots under test, and (b) the number of hugepages before splitting adds
> up to the number of pages across all memslots under test.  (b) is a little
> tenuous as it relies on memslot0 being incompatible with transparent
> hugepages, but that holds true for now as selftests explicitly madvise()
> MADV_NOHUGEPAGE for memslot0 (__vm_create() unconditionally specifies the
> backing type as VM_MEM_SRC_ANONYMOUS).
> 
> Reported-by: Yi Lai <yi1.lai@xxxxxxxxx>
> Reported-by: Tao Su <tao1.su@xxxxxxxxxxxxxxx>
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> ---
>  .../x86_64/dirty_log_page_splitting_test.c    | 21 +++++++++++--------
>  1 file changed, 12 insertions(+), 9 deletions(-)
> 
> diff --git a/tools/testing/selftests/kvm/x86_64/dirty_log_page_splitting_test.c b/tools/testing/selftests/kvm/x86_64/dirty_log_page_splitting_test.c
> index 634c6bfcd572..4864cf3fae57 100644
> --- a/tools/testing/selftests/kvm/x86_64/dirty_log_page_splitting_test.c
> +++ b/tools/testing/selftests/kvm/x86_64/dirty_log_page_splitting_test.c
> @@ -92,7 +92,6 @@ static void run_test(enum vm_guest_mode mode, void *unused)
>  	uint64_t host_num_pages;
>  	uint64_t pages_per_slot;
>  	int i;
> -	uint64_t total_4k_pages;
>  	struct kvm_page_stats stats_populated;
>  	struct kvm_page_stats stats_dirty_logging_enabled;
>  	struct kvm_page_stats stats_dirty_pass[ITERATIONS];
> @@ -107,6 +106,9 @@ static void run_test(enum vm_guest_mode mode, void *unused)
>  	guest_num_pages = vm_adjust_num_guest_pages(mode, guest_num_pages);
>  	host_num_pages = vm_num_host_pages(mode, guest_num_pages);
>  	pages_per_slot = host_num_pages / SLOTS;
> +	TEST_ASSERT_EQ(host_num_pages, pages_per_slot * SLOTS);
> +	TEST_ASSERT(!(host_num_pages % 512),
> +		    "Number of pages, '%lu' not a multiple of 2MiB", host_num_pages);
>  
>  	bitmaps = memstress_alloc_bitmaps(SLOTS, pages_per_slot);
>  
> @@ -165,10 +167,8 @@ static void run_test(enum vm_guest_mode mode, void *unused)
>  	memstress_free_bitmaps(bitmaps, SLOTS);
>  	memstress_destroy_vm(vm);
>  
> -	/* Make assertions about the page counts. */
> -	total_4k_pages = stats_populated.pages_4k;
> -	total_4k_pages += stats_populated.pages_2m * 512;
> -	total_4k_pages += stats_populated.pages_1g * 512 * 512;
> +	TEST_ASSERT_EQ((stats_populated.pages_2m * 512 +
> +			stats_populated.pages_1g * 512 * 512), host_num_pages);
>  
>  	/*
>  	 * Check that all huge pages were split. Since large pages can only
> @@ -180,19 +180,22 @@ static void run_test(enum vm_guest_mode mode, void *unused)
>  	 */
>  	if (dirty_log_manual_caps) {
>  		TEST_ASSERT_EQ(stats_clear_pass[0].hugepages, 0);
> -		TEST_ASSERT_EQ(stats_clear_pass[0].pages_4k, total_4k_pages);
> +		TEST_ASSERT(stats_clear_pass[0].pages_4k >= host_num_pages,
> +			    "Expected at least '%lu' 4KiB pages, found only '%lu'",
> +			    host_num_pages, stats_clear_pass[0].pages_4k);
>  		TEST_ASSERT_EQ(stats_dirty_logging_enabled.hugepages, stats_populated.hugepages);
>  	} else {
>  		TEST_ASSERT_EQ(stats_dirty_logging_enabled.hugepages, 0);
> -		TEST_ASSERT_EQ(stats_dirty_logging_enabled.pages_4k, total_4k_pages);
> +		TEST_ASSERT(stats_dirty_logging_enabled.pages_4k >= host_num_pages,
> +			    "Expected at least '%lu' 4KiB pages, found only '%lu'",
> +			    host_num_pages, stats_clear_pass[0].pages_4k);

Here should print stats_dirty_logging_enabled.pages_4k, not stats_clear_pass[0].pages_4k.

Everything else looks great.

Reviewed-by: Tao Su <tao1.su@xxxxxxxxxxxxxxx>

>  	}
>  
>  	/*
>  	 * Once dirty logging is disabled and the vCPUs have touched all their
> -	 * memory again, the page counts should be the same as they were
> +	 * memory again, the hugepage counts should be the same as they were
>  	 * right after initial population of memory.
>  	 */
> -	TEST_ASSERT_EQ(stats_populated.pages_4k, stats_repopulated.pages_4k);
>  	TEST_ASSERT_EQ(stats_populated.pages_2m, stats_repopulated.pages_2m);
>  	TEST_ASSERT_EQ(stats_populated.pages_1g, stats_repopulated.pages_1g);
>  }
> 
> base-commit: f0f3b810edda57f317d79f452056786257089667
> -- 
> 2.43.0.429.g432eaa2c6b-goog
>