Re: [PATCH] kvm: selftests: aarch64: dirty_log_test: fix unaligned memslot size

[Peter Xu <peterx@redhat.com>]

On Thu, May 23, 2019 at 11:34:05AM +0200, Andrew Jones wrote:
> The memory slot size must be aligned to the host's page size. When
> testing a guest with a 4k page size on a host with a 64k page size,
> then 3 guest pages are not host page size aligned. Since we just need
> a nearly arbitrary number of extra pages to ensure the memslot is not
> aligned to a 64 host-page boundary for this test, then we can use
> 16, as that's 64k aligned, but not 64 * 64k aligned.
> 
> Fixes: 76d58e0f07ec ("KVM: fix KVM_CLEAR_DIRTY_LOG for memory slots of unaligned size", 2019-04-17)
> Signed-off-by: Andrew Jones <drjones@redhat.com>
> 
> ---
> Note, the commit "KVM: fix KVM_CLEAR_DIRTY_LOG for memory slots of
> unaligned size" was somehow committed twice. 76d58e0f07ec is the
> first instance.
> 
>  tools/testing/selftests/kvm/dirty_log_test.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/tools/testing/selftests/kvm/dirty_log_test.c b/tools/testing/selftests/kvm/dirty_log_test.c
> index f50a15c38f9b..bf85afbf1b5f 100644
> --- a/tools/testing/selftests/kvm/dirty_log_test.c
> +++ b/tools/testing/selftests/kvm/dirty_log_test.c
> @@ -292,7 +292,7 @@ static void run_test(enum vm_guest_mode mode, unsigned long iterations,
>  	 * A little more than 1G of guest page sized pages.  Cover the
>  	 * case where the size is not aligned to 64 pages.
>  	 */
> -	guest_num_pages = (1ul << (30 - guest_page_shift)) + 3;
> +	guest_num_pages = (1ul << (30 - guest_page_shift)) + 16;

Hi, Drew,

Could you help explain what's the error on ARM?  Since I still cannot
understand how it failed from the first glance...

Also, even if we want to have the alignment, shall we do the math
using known host/guest page size rather than another adhoc number or
could it still break with some other combinations of host/guest page
sizes?

Thanks,

-- 
Peter Xu