Re: [PATCH v3 2/5] kselftest: vm: Fix mdwe's mmap_FIXED test case

[Ryan Roberts <ryan.roberts@arm.com>]

On 04/07/2023 16:36, Florent Revest wrote:
> I checked with the original author, the mmap_FIXED test case wasn't
> properly tested and fails. Currently, it maps two consecutive (non
> overlapping) pages and expects the second mapping to be denied by MDWE
> but these two pages have nothing to do with each other so MDWE is
> actually out of the picture here.
> 
> What the test actually intended to do was to remap a virtual address
> using MAP_FIXED. However, this operation unmaps the existing mapping and
> creates a new one so the va is backed by a new page and MDWE is again
> out of the picture, all remappings should succeed.
> 
> This patch keeps the test case to make it clear that this situation is
> expected to work.
> 
> Signed-off-by: Florent Revest <revest@chromium.org>
> Reviewed-by: David Hildenbrand <david@redhat.com>
> Fixes: 4cf1fe34fd18 ("kselftest: vm: add tests for memory-deny-write-execute")

I'm currently working to get all the mm selftests running (and ideally passing!)
on arm64 and saw these same spurious failures. Thanks for the patch!

Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>
Tested-by: Ryan Roberts <ryan.roberts@arm.com>


> ---
>  tools/testing/selftests/mm/mdwe_test.c | 9 +++------
>  1 file changed, 3 insertions(+), 6 deletions(-)
> 
> diff --git a/tools/testing/selftests/mm/mdwe_test.c b/tools/testing/selftests/mm/mdwe_test.c
> index d0954c657feb..91aa9c3099e7 100644
> --- a/tools/testing/selftests/mm/mdwe_test.c
> +++ b/tools/testing/selftests/mm/mdwe_test.c
> @@ -168,13 +168,10 @@ TEST_F(mdwe, mmap_FIXED)
>  	self->p = mmap(NULL, self->size, PROT_READ, self->flags, 0, 0);
>  	ASSERT_NE(self->p, MAP_FAILED);
>  
> -	p = mmap(self->p + self->size, self->size, PROT_READ | PROT_EXEC,
> +	/* MAP_FIXED unmaps the existing page before mapping which is allowed */
> +	p = mmap(self->p, self->size, PROT_READ | PROT_EXEC,
>  		 self->flags | MAP_FIXED, 0, 0);
> -	if (variant->enabled) {
> -		EXPECT_EQ(p, MAP_FAILED);
> -	} else {
> -		EXPECT_EQ(p, self->p);
> -	}
> +	EXPECT_EQ(p, self->p);
>  }
>  
>  TEST_F(mdwe, arm64_BTI)