Re: [PATCH 5/5] selftests/xsk: Introduce mmap_size in umem struct

[sashiko-bot@kernel.org]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] Meaningful code and commit message mismatch regarding `mmap_size` computation, failing to resolve the over-unmapping risk.
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commit 88aa7962c655c10bde2c97d706550190e3d87126
Author: Tushar Vyavahare <tushar.vyavahare@intel.com>

selftests/xsk: Introduce mmap_size in umem struct

This commit stores the finalized mapping length in xsk_umem_info as mmap_size
when the UMEM mapping is created. The intent is to use this exact value during
teardown instead of recomputing it from the frame geometry.

> diff --git a/tools/testing/selftests/bpf/prog_tests/test_xsk.c b/tools/testing/selftests/bpf/prog_tests/test_xsk.c
> index ba4768f83eb6..ba1bcfc6b74b 100644
> --- a/tools/testing/selftests/bpf/prog_tests/test_xsk.c
> +++ b/tools/testing/selftests/bpf/prog_tests/test_xsk.c
[ ... ]
> @@ -1594,6 +1594,8 @@ static int thread_common_ops(struct test_spec *test, struct ifobject *ifobject)
>  	if (bufs == MAP_FAILED)
>  		return -errno;
>  
> +	umem->mmap_size = ceil_u64(umem_sz, HUGEPAGE_SIZE) * HUGEPAGE_SIZE;
> +
>  	ret = xsk_configure_umem(ifobject, umem, bufs, umem_sz);
>  	if (ret)
>  		return ret;

The commit message states that this change "removes duplicated size
arithmetic in cleanup and guarantees that munmap() uses the same canonical
size that was established at setup time."

However, looking earlier in thread_common_ops():

	bufs = mmap(NULL, umem_sz, PROT_READ | PROT_WRITE, mmap_flags, -1, 0);

The size passed to mmap() is just umem_sz, without the hugepage rounding.

By setting umem->mmap_size to the rounded-up value here, does this still
duplicate the size arithmetic rather than using the exact mapping metadata?

If standard pages are used and umem_sz is not a multiple of HUGEPAGE_SIZE,
could this cause munmap() to use an inflated size and inadvertently unmap
adjacent memory?

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Sashiko AI review · https://sashiko.dev/#/patchset/20260428080317.702124-1-tushar.vyavahare@intel.com?part=5