[PATCH] selftests/mm: remove obsolete hugetlb vmemmap test

[PATCH] selftests/mm: remove obsolete hugetlb vmemmap test

[Muchun Song]

The hugetlb vmemmap selftest was added to check the old HVO
layout where tail vmemmap pages reused the head page.  That
assumption no longer matches the current HVO mapping layout.

HVO now keeps a private backing page for the head vmemmap page
and remaps redundant tail vmemmap pages to a shared read-only
backing page.  The old page flag check is therefore testing an
obsolete implementation detail rather than the current ABI or
behavior.

Remove the stale test and its build, run, and ignore entries.

Signed-off-by: Muchun Song <songmuchun@bytedance.com>
---
 tools/testing/selftests/mm/.gitignore        |   2 -
 tools/testing/selftests/mm/Makefile          |   1 -
 tools/testing/selftests/mm/hugetlb-vmemmap.c | 132 -------------------
 tools/testing/selftests/mm/run_vmtests.sh    |   1 -
 4 files changed, 136 deletions(-)
 delete mode 100644 tools/testing/selftests/mm/hugetlb-vmemmap.c

diff --git a/tools/testing/selftests/mm/.gitignore b/tools/testing/selftests/mm/.gitignore
index 9ccd9e1447e6..227476d8ff1f 100644
--- a/tools/testing/selftests/mm/.gitignore
+++ b/tools/testing/selftests/mm/.gitignore
@@ -3,11 +3,9 @@ cow
 hugepage-mmap
 hugepage-mremap
 hugepage-shm
-hugepage-vmemmap
 hugetlb-mmap
 hugetlb-mremap
 hugetlb-shm
-hugetlb-vmemmap
 hugetlb-madvise
 hugetlb-read-hwpoison
 hugetlb-soft-offline
diff --git a/tools/testing/selftests/mm/Makefile b/tools/testing/selftests/mm/Makefile
index ed321ae709da..ee8def9b4c31 100644
--- a/tools/testing/selftests/mm/Makefile
+++ b/tools/testing/selftests/mm/Makefile
@@ -66,7 +66,6 @@ TEST_GEN_FILES += hugetlb-mremap
 TEST_GEN_FILES += hugetlb-read-hwpoison
 TEST_GEN_FILES += hugetlb-shm
 TEST_GEN_FILES += hugetlb-soft-offline
-TEST_GEN_FILES += hugetlb-vmemmap
 TEST_GEN_FILES += khugepaged
 TEST_GEN_FILES += madv_populate
 TEST_GEN_FILES += map_fixed_noreplace
diff --git a/tools/testing/selftests/mm/hugetlb-vmemmap.c b/tools/testing/selftests/mm/hugetlb-vmemmap.c
deleted file mode 100644
index 507df78a158d..000000000000
--- a/tools/testing/selftests/mm/hugetlb-vmemmap.c
+++ /dev/null
@@ -1,132 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0
-/*
- * A test case of using hugepage memory in a user application using the
- * mmap system call with MAP_HUGETLB flag.  Before running this program
- * make sure the administrator has allocated enough default sized huge
- * pages to cover the 2 MB allocation.
- */
-#include <stdlib.h>
-#include <stdio.h>
-#include <unistd.h>
-#include <sys/mman.h>
-#include <fcntl.h>
-#include "vm_util.h"
-#include "hugepage_settings.h"
-
-#define PAGE_COMPOUND_HEAD	(1UL << 15)
-#define PAGE_COMPOUND_TAIL	(1UL << 16)
-#define PAGE_HUGE		(1UL << 17)
-
-#define HEAD_PAGE_FLAGS		(PAGE_COMPOUND_HEAD | PAGE_HUGE)
-#define TAIL_PAGE_FLAGS		(PAGE_COMPOUND_TAIL | PAGE_HUGE)
-
-#define PM_PFRAME_BITS		55
-#define PM_PFRAME_MASK		~((1UL << PM_PFRAME_BITS) - 1)
-
-static size_t pagesize;
-static size_t maplength;
-
-static void write_bytes(char *addr, size_t length)
-{
-	unsigned long i;
-
-	for (i = 0; i < length; i++)
-		*(addr + i) = (char)i;
-}
-
-static unsigned long virt_to_pfn(void *addr)
-{
-	int fd;
-	unsigned long pagemap;
-
-	fd = open("/proc/self/pagemap", O_RDONLY);
-	if (fd < 0)
-		return -1UL;
-
-	lseek(fd, (unsigned long)addr / pagesize * sizeof(pagemap), SEEK_SET);
-	read(fd, &pagemap, sizeof(pagemap));
-	close(fd);
-
-	return pagemap & ~PM_PFRAME_MASK;
-}
-
-static int check_page_flags(unsigned long pfn)
-{
-	int fd, i;
-	unsigned long pageflags;
-
-	fd = open("/proc/kpageflags", O_RDONLY);
-	if (fd < 0)
-		return -1;
-
-	lseek(fd, pfn * sizeof(pageflags), SEEK_SET);
-
-	read(fd, &pageflags, sizeof(pageflags));
-	if ((pageflags & HEAD_PAGE_FLAGS) != HEAD_PAGE_FLAGS) {
-		close(fd);
-		ksft_print_msg("Head page flags (%lx) is invalid\n", pageflags);
-		return -1;
-	}
-
-	/*
-	 * pages other than the first page must be tail and shouldn't be head;
-	 * this also verifies kernel has correctly set the fake page_head to tail
-	 * while hugetlb_free_vmemmap is enabled.
-	 */
-	for (i = 1; i < maplength / pagesize; i++) {
-		read(fd, &pageflags, sizeof(pageflags));
-		if ((pageflags & TAIL_PAGE_FLAGS) != TAIL_PAGE_FLAGS ||
-		    (pageflags & HEAD_PAGE_FLAGS) == HEAD_PAGE_FLAGS) {
-			close(fd);
-			ksft_print_msg("Tail page flags (%lx) is invalid\n", pageflags);
-			return -1;
-		}
-	}
-
-	close(fd);
-
-	return 0;
-}
-
-int main(int argc, char **argv)
-{
-	void *addr;
-	unsigned long pfn;
-	int ret;
-
-	ksft_print_header();
-	ksft_set_plan(1);
-
-	if (!hugetlb_setup_default(1))
-		ksft_exit_skip("Not enough free huge pages\n");
-
-	pagesize  = psize();
-	maplength = default_huge_page_size();
-	if (!maplength)
-		ksft_exit_skip("Unable to determine huge page size\n");
-
-	addr = mmap(NULL, maplength, PROT_READ | PROT_WRITE,
-			MAP_PRIVATE | MAP_ANONYMOUS | MAP_HUGETLB, -1, 0);
-	if (addr == MAP_FAILED)
-		ksft_exit_fail_perror("mmap");
-
-	/* Trigger allocation of HugeTLB page. */
-	write_bytes(addr, maplength);
-
-	pfn = virt_to_pfn(addr);
-	if (pfn == -1UL) {
-		ksft_perror("virt_to_pfn");
-		munmap(addr, maplength);
-		ksft_exit_fail();
-	}
-
-	ksft_print_msg("Returned address is %p whose pfn is %lx\n", addr, pfn);
-
-	ret = check_page_flags(pfn);
-
-	if (munmap(addr, maplength))
-		ksft_exit_fail_perror("munmap");
-
-	ksft_test_result(!ret, "HugeTLB vmemmap page flags\n");
-	ksft_finished();
-}
diff --git a/tools/testing/selftests/mm/run_vmtests.sh b/tools/testing/selftests/mm/run_vmtests.sh
index 8c296dedf047..a60b9f9f16e7 100755
--- a/tools/testing/selftests/mm/run_vmtests.sh
+++ b/tools/testing/selftests/mm/run_vmtests.sh
@@ -262,7 +262,6 @@ echo "TAP version 13" | tap_output
 CATEGORY="hugetlb" run_test ./hugetlb-mmap
 CATEGORY="hugetlb" run_test ./hugetlb-shm
 CATEGORY="hugetlb" run_test ./hugetlb-mremap
-CATEGORY="hugetlb" run_test ./hugetlb-vmemmap
 CATEGORY="hugetlb" run_test ./hugetlb-madvise
 CATEGORY="hugetlb" run_test ./hugetlb_dio
 CATEGORY="hugetlb" run_test ./hugetlb_fault_after_madv

base-commit: 4f441960e691d37c880d2cc004de06bb5b6bd5e4
-- 
2.54.0

Re: [PATCH] selftests/mm: remove obsolete hugetlb vmemmap test

[Lorenzo Stoakes]

On Fri, 10 Jul 2026 17:24:27 +0800, Muchun Song <songmuchun@bytedance.com> wrote:
> The hugetlb vmemmap selftest was added to check the old HVO
> layout where tail vmemmap pages reused the head page.  That
> assumption no longer matches the current HVO mapping layout.
> 
> HVO now keeps a private backing page for the head vmemmap page
> and remaps redundant tail vmemmap pages to a shared read-only
> backing page.  The old page flag check is therefore testing an
> obsolete implementation detail rather than the current ABI or
> behavior.
> 
> Remove the stale test and its build, run, and ignore entries.
> 
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>

LGTM, always happy to see red in the diffstat! And we definitely do not want a
test testing something that isn't real (...!).

>
>
> diff --git a/tools/testing/selftests/mm/.gitignore b/tools/testing/selftests/mm/.gitignore
> index 9ccd9e1447e6..227476d8ff1f 100644
> --- a/tools/testing/selftests/mm/.gitignore
> +++ b/tools/testing/selftests/mm/.gitignore
> @@ -3,11 +3,9 @@ cow
>  hugepage-mmap
>  hugepage-mremap
>  hugepage-shm
> -hugepage-vmemmap
>  hugetlb-mmap
>  hugetlb-mremap
>  hugetlb-shm
> -hugetlb-vmemmap

It was here twice :) wow.

Reviewed-by: Lorenzo Stoakes <ljs@kernel.org>

-- 
Lorenzo Stoakes <ljs@kernel.org>

Re: [PATCH] selftests/mm: remove obsolete hugetlb vmemmap test

[David Hildenbrand (Arm)]

On 7/10/26 11:24, Muchun Song wrote:
> The hugetlb vmemmap selftest was added to check the old HVO
> layout where tail vmemmap pages reused the head page.  That
> assumption no longer matches the current HVO mapping layout.
> 
> HVO now keeps a private backing page for the head vmemmap page
> and remaps redundant tail vmemmap pages to a shared read-only
> backing page.  The old page flag check is therefore testing an
> obsolete implementation detail rather than the current ABI or
> behavior.
> 
> Remove the stale test and its build, run, and ignore entries.
> 
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>
> ---

Acked-by: David Hildenbrand (Arm) <david@kernel.org>

-- 
Cheers,

David

Re: [PATCH] selftests/mm: remove obsolete hugetlb vmemmap test

[SJ Park]

On Fri, 10 Jul 2026 17:24:27 +0800 Muchun Song <songmuchun@bytedance.com> wrote:

> The hugetlb vmemmap selftest was added to check the old HVO
> layout where tail vmemmap pages reused the head page.  That
> assumption no longer matches the current HVO mapping layout.
> 
> HVO now keeps a private backing page for the head vmemmap page
> and remaps redundant tail vmemmap pages to a shared read-only
> backing page.  The old page flag check is therefore testing an
> obsolete implementation detail rather than the current ABI or
> behavior.
> 
> Remove the stale test and its build, run, and ignore entries.

Nice!

> 
> Signed-off-by: Muchun Song <songmuchun@bytedance.com>

Reviewed-by: SJ Park <sj@kernel.org>

> ---
>  tools/testing/selftests/mm/.gitignore        |   2 -
>  tools/testing/selftests/mm/Makefile          |   1 -
>  tools/testing/selftests/mm/hugetlb-vmemmap.c | 132 -------------------
>  tools/testing/selftests/mm/run_vmtests.sh    |   1 -
>  4 files changed, 136 deletions(-)
>  delete mode 100644 tools/testing/selftests/mm/hugetlb-vmemmap.c
> 
> diff --git a/tools/testing/selftests/mm/.gitignore b/tools/testing/selftests/mm/.gitignore
> index 9ccd9e1447e6..227476d8ff1f 100644
> --- a/tools/testing/selftests/mm/.gitignore
> +++ b/tools/testing/selftests/mm/.gitignore
> @@ -3,11 +3,9 @@ cow
>  hugepage-mmap
>  hugepage-mremap
>  hugepage-shm
> -hugepage-vmemmap
>  hugetlb-mmap
>  hugetlb-mremap
>  hugetlb-shm
> -hugetlb-vmemmap
>  hugetlb-madvise
>  hugetlb-read-hwpoison
>  hugetlb-soft-offline

I remember Linus argued [1] we shouldn't remove names from giignore.  I don't
really care, so feel free to add my R-b: tag.  I just wanted to call out,
though.

[1] https://lore.kernel.org/all/CAHk-=whVY4mq1Fd=Vhwy0dK8fR5cOLkiy1OZMG4QyEMaGEd9ZQ@mail.gmail.com/


Thanks,
SJ

[...]