Re: [PATCH v3 3/3] selftests/mm: fix va_high_addr_switch.sh failure on x86_64

[David Hildenbrand <david@redhat.com>]

On 12.09.25 03:37, Chunyu Hu wrote:
> The test will fail as below on x86_64 with cpu la57 support (will skip if
> no la57 support). Note, the test requries nr_hugepages to be set first.
> 
>    # running bash ./va_high_addr_switch.sh
>    # -------------------------------------
>    # mmap(addr_switch_hint - pagesize, pagesize): 0x7f55b60fa000 - OK
>    # mmap(addr_switch_hint - pagesize, (2 * pagesize)): 0x7f55b60f9000 - OK
>    # mmap(addr_switch_hint, pagesize): 0x800000000000 - OK
>    # mmap(addr_switch_hint, 2 * pagesize, MAP_FIXED): 0x800000000000 - OK
>    # mmap(NULL): 0x7f55b60f9000 - OK
>    # mmap(low_addr): 0x40000000 - OK
>    # mmap(high_addr): 0x1000000000000 - OK
>    # mmap(high_addr) again: 0xffff55b6136000 - OK
>    # mmap(high_addr, MAP_FIXED): 0x1000000000000 - OK
>    # mmap(-1): 0xffff55b6134000 - OK
>    # mmap(-1) again: 0xffff55b6132000 - OK
>    # mmap(addr_switch_hint - pagesize, pagesize): 0x7f55b60fa000 - OK
>    # mmap(addr_switch_hint - pagesize, 2 * pagesize): 0x7f55b60f9000 - OK
>    # mmap(addr_switch_hint - pagesize/2 , 2 * pagesize): 0x7f55b60f7000 - OK
>    # mmap(addr_switch_hint, pagesize): 0x800000000000 - OK
>    # mmap(addr_switch_hint, 2 * pagesize, MAP_FIXED): 0x800000000000 - OK
>    # mmap(NULL, MAP_HUGETLB): 0x7f55b5c00000 - OK
>    # mmap(low_addr, MAP_HUGETLB): 0x40000000 - OK
>    # mmap(high_addr, MAP_HUGETLB): 0x1000000000000 - OK
>    # mmap(high_addr, MAP_HUGETLB) again: 0xffff55b5e00000 - OK
>    # mmap(high_addr, MAP_FIXED | MAP_HUGETLB): 0x1000000000000 - OK
>    # mmap(-1, MAP_HUGETLB): 0x7f55b5c00000 - OK
>    # mmap(-1, MAP_HUGETLB) again: 0x7f55b5a00000 - OK
>    # mmap(addr_switch_hint - pagesize, 2*hugepagesize, MAP_HUGETLB): 0x800000000000 - FAILED
>    # mmap(addr_switch_hint , 2*hugepagesize, MAP_FIXED | MAP_HUGETLB): 0x800000000000 - OK
>    # [FAIL]
> 
> addr_switch_hint is defined as DFEFAULT_MAP_WINDOW in the failed test (for
> x86_64, DFEFAULT_MAP_WINDOW is defined as (1UL<<47) - pagesize) in 64 bit.
> 
> Before commit cc92882ee218 ("mm: drop hugetlb_get_unmapped_area{_*}
> functions"), for x86_64 hugetlb_get_unmapped_area() is handled in arch code
> arch/x86/mm/hugetlbpage.c and addr is checked with map_address_hint_valid()
> after align with 'addr &= huge_page_mask(h)' which is a round down way, and
> it will fail the check because the addr is within the DEFAULT_MAP_WINDOW but
> (addr + len) is above the DFEFAULT_MAP_WINDOW. So it wil go through the
> hugetlb_get_unmmaped_area_top_down() to find an area within the
> DFEFAULT_MAP_WINDOW.
> 
> After commit cc92882ee218 ("mm: drop hugetlb_get_unmapped_area{_*}
> functions").  The addr hint for hugetlb_get_unmmaped_area() will be rounded
> up and aligned to hugepage size with ALIGN() for all arches.  And after the
> align, the addr will be above the default MAP_DEFAULT_WINDOW, and the
> map_addresshint_valid() check will pass because both aligned addr (addr0)
> and (addr + len) are above the DEFAULT_MAP_WINDOW, and the aligned hint
> address (0x800000000000) is returned as an suitable gap is found there,
> in arch_get_unmapped_area_topdown().
> 
> To still cover the case that addr is within the DEFAULT_MAP_WINDOW, and
> addr + len is above the DFEFAULT_MAP_WINDOW, change to choose the last
> hugepage aligned address within the DEFAULT_MAP_WINDOW as the hint addr,
> and the addr + len (2 hugepages) will be one hugepage above the
> DEFAULT_MAP_WINDOW.  An aligned address won't be affected by the page
> round up or round down from kernel, so it's determistic.
> 
> Fixes: cc92882ee218 ("mm: drop hugetlb_get_unmapped_area{_*} functions")
> Suggested-by: David Hildenbrand <david@redhat.com>
> Signed-off-by: Chunyu Hu <chuhu@redhat.com>
> ---

Acked-by: David Hildenbrand <david@redhat.com>

-- 
Cheers

David / dhildenb