Re: [PATCH v2 2/3] KVM: selftests: arm64: Skip sea_to_user without 1GB hugepages

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Medium] get_free_hugepages() overestimates available hugepages by ignoring reserved pages, which allows the test to proceed and crash with ENOMEM on systems with reserved pools.
--

--- Patch [2]: [PATCH v2 2/3] KVM: selftests: arm64: Skip sea_to_user without 1GB hugepages ---
commit 5fa5666824342b3dd28a5ef6a04bb5ac183257c8
Author: Like Xu <[email protected]>

KVM: selftests: arm64: Skip sea_to_user without 1GB hugepages

This commit adds a check to skip the sea_to_user test if the host does not
have enough 1GB hugepages available, preventing a hard failure on systems
without an empty pool.

[ ... ]
> diff --git a/tools/testing/selftests/kvm/lib/test_util.c b/tools/testing/selftests/kvm/lib/test_util.c
> index bab1bd2b775b6..29f9c1d60b1b7 100644
> --- a/tools/testing/selftests/kvm/lib/test_util.c
> +++ b/tools/testing/selftests/kvm/lib/test_util.c
> @@ -222,6 +222,21 @@ size_t get_def_hugetlb_pagesz(void)
>  	TEST_FAIL("Error in reading /proc/meminfo");
>  }
>  
> +size_t get_free_hugepages(size_t page_size)
> +{
> +	char path[128];
> +	size_t free;
> +
> +	snprintf(path, sizeof(path),
> +		 "/sys/kernel/mm/hugepages/hugepages-%zukB/free_hugepages",
> +		 page_size >> 10);
> +	if (!test_sysfs_path(path))
> +		return 0;
> +
> +	free = get_sysfs_val(path);
> +	return free * page_size;

[Severity: Medium]
Does this calculation overestimate the available hugepages by ignoring the
reserved pool?

The sysfs free_hugepages value includes pages that are already committed to
other mappings but not yet allocated (which are tracked via resv_hugepages). 

If the test runs on a host where free_hugepages meets the VM_MEM_SIZE
requirement but some or all of those pages are reserved, the test will
incorrectly proceed and still crash with an -ENOMEM abort instead of cleanly
skipping.

Could we also read and subtract resv_hugepages to determine the actual
allocatable count?

> +}
> +
>  #define ANON_FLAGS	(MAP_PRIVATE | MAP_ANONYMOUS)
>  #define ANON_HUGE_FLAGS	(ANON_FLAGS | MAP_HUGETLB)
>

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/[email protected]?part=2