Re: [PATCH] mm: make MEMFD_CREATE into a selectable config option

Zhangjin Wu
2023-06-30T13:39:00Z

Hi, Thomas

I have manually applied your patch on v6.4, enabled MEMFD_CREATE (and disabled
TMPFS and HUGETLBFS) for 3 randomly selected virtual boards:

- arm/vexpress-a9
- aarch64/virt
- mipsel/malta

For all of the above boards, the current vfprintf test (uses
memfd_create) of tools/testing/selftests/nolibc/nolibc-test.c passes
without any failure:

Running test 'vfprintf'
0 emptymemfd_create() without MFD_EXEC nor MFD_NOEXEC_SEAL, pid=1 'init'
"" = "" [OK]
1 simple "foo" = "foo" [OK]
2 string "foo" = "foo" [OK]
3 number "1234" = "1234" [OK]
4 negnumber "-1234" = "-1234" [OK]
5 unsigned "12345" = "12345" [OK]
6 char "c" = "c" [OK]
7 hex "f" = "f" [OK]
8 pointer "0x1" = "0x1" [OK]
Errors during this test: 0

If this test result is ok for you, here is my:

Tested-by: Zhangjin Wu <falcon@tinylab.org>

Best regards,
Zhangjin

>
> The memfd_create() syscall, enabled by CONFIG_MEMFD_CREATE, is useful on
> its own even when not required by CONFIG_TMPFS or CONFIG_HUGETLBFS.
>
> Split it into its own proper bool option that can be enabled by users.
>
> Move that option into mm/ where the code itself also lies.
> Also add "select" statements to CONFIG_TMPFS and CONFIG_HUGETLBFS so
> they automatically enable CONFIG_MEMFD_CREATE as before.
>
> Signed-off-by: Thomas Weißschuh <linux@weissschuh.net>
> ---
> fs/Kconfig | 5 ++---
> mm/Kconfig | 3 +++
> 2 files changed, 5 insertions(+), 3 deletions(-)
>
> diff --git a/fs/Kconfig b/fs/Kconfig
> index 18d034ec7953..19975b104bc3 100644
> --- a/fs/Kconfig
> +++ b/fs/Kconfig
> @@ -169,6 +169,7 @@ source "fs/sysfs/Kconfig"
> config TMPFS
> bool "Tmpfs virtual memory file system support (former shm fs)"
> depends on SHMEM
> + select MEMFD_CREATE
> help
> Tmpfs is a file system which keeps all files in virtual memory.
>
> @@ -240,6 +241,7 @@ config HUGETLBFS
> bool "HugeTLB file system support"
> depends on X86 || IA64 || SPARC64 || ARCH_SUPPORTS_HUGETLBFS || BROKEN
> depends on (SYSFS || SYSCTL)
> + select MEMFD_CREATE
> help
> hugetlbfs is a filesystem backing for HugeTLB pages, based on
> ramfs. For architectures that support it, say Y here and read
> @@ -264,9 +266,6 @@ config HUGETLB_PAGE_OPTIMIZE_VMEMMAP_DEFAULT_ON
> enable HVO by default. It can be disabled via hugetlb_free_vmemmap=off
> (boot command line) or hugetlb_optimize_vmemmap (sysctl).
>
> -config MEMFD_CREATE
> - def_bool TMPFS || HUGETLBFS
> -
> config ARCH_HAS_GIGANTIC_PAGE
> bool
>
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 09130434e30d..22acffd9009d 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -1144,6 +1144,9 @@ config KMAP_LOCAL_NON_LINEAR_PTE_ARRAY
> config IO_MAPPING
> bool
>
> +config MEMFD_CREATE
> + bool "Enable memfd_create() system call" if EXPERT
> +
> config SECRETMEM
> default y
> bool "Enable memfd_secret() system call" if EXPERT
>
> ---
> base-commit: e55e5df193d247a38a5e1ac65a5316a0adcc22fa
> change-id: 20230629-config-memfd-be6af03b7dca
>
> Best regards,
> --
> Thomas Weißschuh <linux@weissschuh.net>
>