[RFC PATCH 0/2] Add flag as THP allocation hint for memfd_restricted() syscall

Hello,

This patchset builds upon the memfd_restricted() system call that has
been discussed in the ‘KVM: mm: fd-based approach for supporting KVM’
patch series, at
https://lore.kernel.org/lkml/20221202061347.1070246-1-chao.p.peng@linux.intel.com/T/#m7e944d7892afdd1d62a03a287bd488c56e377b0c

The tree can be found at:
https://github.com/googleprodkernel/linux-cc/tree/restrictedmem-rmfd-hugepage

Following the RFC to provide mount for memfd_restricted() syscall at
https://lore.kernel.org/lkml/cover.1676507663.git.ackerleytng@google.com/T/#u,
this patchset adds the RMFD_HUGEPAGE flag to the memfd_restricted()
syscall, which will hint the kernel to use Transparent HugePages to
back restrictedmem pages.

This supplements the interface proposed earlier, which requires the
creation of a tmpfs mount to be passed to memfd_restricted(), with a
more direct per-file hint.

Dependencies:

+ Sean’s iteration of the ‘KVM: mm: fd-based approach for supporting
  KVM’ patch series at
  https://github.com/sean-jc/linux/tree/x86/upm_base_support
+ Proposed fix for restrictedmem_getattr() as mentioned on the mailing
  list at
  https://lore.kernel.org/lkml/diqzzga0fv96.fsf@ackerleytng-cloudtop-sg.c.googlers.com/
+ Hugh’s patch:
  https://lore.kernel.org/lkml/c140f56a-1aa3-f7ae-b7d1-93da7d5a3572@google.com/,
  which provides functionality in shmem that reads the VM_HUGEPAGE
  flag in key functions shmem_is_huge() and shmem_get_inode()

Future work/TODOs:
+ man page for the memfd_restricted() syscall
+ Support for per file NUMA binding hints

Ackerley Tng (2):
  mm: restrictedmem: Add flag as THP allocation hint for
    memfd_restricted() syscall
  selftests: restrictedmem: Add selftest for RMFD_HUGEPAGE

 include/uapi/linux/restrictedmem.h            |  1 +
 mm/restrictedmem.c                            | 27 ++++++++++++-------
 .../restrictedmem_hugepage_test.c             | 25 +++++++++++++++++
 3 files changed, 43 insertions(+), 10 deletions(-)

--
2.39.2.637.g21b0678d19-goog

Allow userspace to hint the kernel to use Transparent HugePages to
back restricted memory on a per-file basis.

Signed-off-by: Ackerley Tng <redacted>
---
 include/uapi/linux/restrictedmem.h |  1 +
 mm/restrictedmem.c                 | 27 +++++++++++++++++----------
 2 files changed, 18 insertions(+), 10 deletions(-)

diff --git a/include/uapi/linux/restrictedmem.h b/include/uapi/linux/restrictedmem.h
index 9f108dd1ac4c..f671ccbb43bc 100644
--- a/include/uapi/linux/restrictedmem.h
+++ b/include/uapi/linux/restrictedmem.h

@@ -4,5 +4,6 @@
 
 /* flags for memfd_restricted */
 #define RMFD_TMPFILE		0x0001U
+#define RMFD_HUGEPAGE		0x0002U
 
 #endif /* _UAPI_LINUX_RESTRICTEDMEM_H */

diff --git a/mm/restrictedmem.c b/mm/restrictedmem.c
index 97f3e2159e8b..87c829960b31 100644
--- a/mm/restrictedmem.c
+++ b/mm/restrictedmem.c

@@ -190,19 +190,25 @@ static struct file *restrictedmem_file_create(struct file *memfd)
 	return file;
 }
 
-static int restrictedmem_create(struct vfsmount *mount)
+static int restrictedmem_create(unsigned int flags, struct vfsmount *mount)
 {
 	struct file *file, *restricted_file;
 	int fd, err;
+	unsigned long shmem_setup_flags = VM_NORESERVE;
 
 	fd = get_unused_fd_flags(0);
 	if (fd < 0)
 		return fd;
 
-	if (mount)
-		file = shmem_file_setup_with_mnt(mount, "memfd:restrictedmem", 0, VM_NORESERVE);
-	else
-		file = shmem_file_setup("memfd:restrictedmem", 0, VM_NORESERVE);
+	if (flags & RMFD_HUGEPAGE)
+		shmem_setup_flags |= VM_HUGEPAGE;
+
+	if (mount) {
+		file = shmem_file_setup_with_mnt(mount, "memfd:restrictedmem",
+						 0, shmem_setup_flags);
+	} else {
+		file = shmem_file_setup("memfd:restrictedmem", 0, shmem_setup_flags);
+	}
 
 	if (IS_ERR(file)) {
 		err = PTR_ERR(file);

@@ -230,7 +236,8 @@ static bool is_shmem_mount(struct vfsmount *mnt)
 	return mnt->mnt_sb->s_magic == TMPFS_MAGIC;
 }
 
-static int restrictedmem_create_from_path(const char __user *mount_path)
+static int restrictedmem_create_from_path(unsigned int flags,
+					  const char __user *mount_path)
 {
 	int ret;
 	struct path path;

@@ -250,7 +257,7 @@ static int restrictedmem_create_from_path(const char __user *mount_path)
 	if (unlikely(ret))
 		goto out;
 
-	ret = restrictedmem_create(path.mnt);
+	ret = restrictedmem_create(flags, path.mnt);
 
 	mnt_drop_write(path.mnt);
 out:

@@ -261,16 +268,16 @@ static int restrictedmem_create_from_path(const char __user *mount_path)
 
 SYSCALL_DEFINE2(memfd_restricted, unsigned int, flags, const char __user *, mount_path)
 {
-	if (flags & ~RMFD_TMPFILE)
+	if (flags & ~(RMFD_TMPFILE | RMFD_HUGEPAGE))
 		return -EINVAL;
 
 	if (flags == RMFD_TMPFILE) {
 		if (!mount_path)
 			return -EINVAL;
 
-		return restrictedmem_create_from_path(mount_path);
+		return restrictedmem_create_from_path(flags, mount_path);
 	} else {
-		return restrictedmem_create(NULL);
+		return restrictedmem_create(flags, NULL);
 	}
 }
 

-- 
2.39.2.637.g21b0678d19-goog

Tests that when RMFD_HUGEPAGE is specified, restrictedmem will be
backed by Transparent HugePages.

Signed-off-by: Ackerley Tng <redacted>
---
 .../restrictedmem_hugepage_test.c             | 25 +++++++++++++++++++
 1 file changed, 25 insertions(+)

diff --git a/tools/testing/selftests/restrictedmem/restrictedmem_hugepage_test.c b/tools/testing/selftests/restrictedmem/restrictedmem_hugepage_test.c
index 0d9cf2ced754..75283d68696f 100644
--- a/tools/testing/selftests/restrictedmem/restrictedmem_hugepage_test.c
+++ b/tools/testing/selftests/restrictedmem/restrictedmem_hugepage_test.c

@@ -180,6 +180,31 @@ TEST_F(reset_shmem_enabled, restrictedmem_fstat_shmem_enabled_always)
 	close(mfd);
 }
 
+TEST(restrictedmem_invalid_flags)
+{
+	int mfd = memfd_restricted(99, NULL);
+
+	ASSERT_EQ(-1, mfd);
+	ASSERT_EQ(EINVAL, errno);
+}
+
+TEST_F(reset_shmem_enabled, restrictedmem_rmfd_hugepage)
+{
+	int mfd = -1;
+	struct stat stat;
+
+	ASSERT_EQ(0, set_shmem_thp_policy("never"));
+
+	mfd = memfd_restricted(RMFD_HUGEPAGE, NULL);
+	ASSERT_NE(-1, mfd);
+
+	ASSERT_EQ(0, fstat(mfd, &stat));
+
+	ASSERT_EQ(stat.st_blksize, get_hpage_pmd_size());
+
+	close(mfd);
+}
+
 TEST(restrictedmem_tmpfile_no_mount_path)
 {
 	int mfd = memfd_restricted(RMFD_TMPFILE, NULL);

-- 
2.39.2.637.g21b0678d19-goog

On Sat, Feb 18, 2023 at 12:43:00AM +0000, Ackerley Tng wrote:

Hello,

This patchset builds upon the memfd_restricted() system call that has
been discussed in the ‘KVM: mm: fd-based approach for supporting KVM’
patch series, at
https://lore.kernel.org/lkml/20221202061347.1070246-1-chao.p.peng@linux.intel.com/T/#m7e944d7892afdd1d62a03a287bd488c56e377b0c

The tree can be found at:
https://github.com/googleprodkernel/linux-cc/tree/restrictedmem-rmfd-hugepage

Following the RFC to provide mount for memfd_restricted() syscall at
https://lore.kernel.org/lkml/cover.1676507663.git.ackerleytng@google.com/T/#u,
this patchset adds the RMFD_HUGEPAGE flag to the memfd_restricted()
syscall, which will hint the kernel to use Transparent HugePages to
back restrictedmem pages.

This supplements the interface proposed earlier, which requires the
creation of a tmpfs mount to be passed to memfd_restricted(), with a
more direct per-file hint.

Dependencies:

+ Sean’s iteration of the ‘KVM: mm: fd-based approach for supporting
  KVM’ patch series at
  https://github.com/sean-jc/linux/tree/x86/upm_base_support
+ Proposed fix for restrictedmem_getattr() as mentioned on the mailing
  list at
  https://lore.kernel.org/lkml/diqzzga0fv96.fsf@ackerleytng-cloudtop-sg.c.googlers.com/
+ Hugh’s patch:
  https://lore.kernel.org/lkml/c140f56a-1aa3-f7ae-b7d1-93da7d5a3572@google.com/,
  which provides functionality in shmem that reads the VM_HUGEPAGE
  flag in key functions shmem_is_huge() and shmem_get_inode()

Will Hugh's patch be merged into 6.3 ? I didn't find it in 6.2-rc8.
IMHO this patch won't work without Hugh's patch, or at least need
another way, e.g. HMEM_SB(inode->i_sb)->huge.

Future work/TODOs:
+ man page for the memfd_restricted() syscall
+ Support for per file NUMA binding hints

Ackerley Tng (2):
  mm: restrictedmem: Add flag as THP allocation hint for
    memfd_restricted() syscall
  selftests: restrictedmem: Add selftest for RMFD_HUGEPAGE

 include/uapi/linux/restrictedmem.h            |  1 +
 mm/restrictedmem.c                            | 27 ++++++++++++-------
 .../restrictedmem_hugepage_test.c             | 25 +++++++++++++++++
 3 files changed, 43 insertions(+), 10 deletions(-)

--
2.39.2.637.g21b0678d19-goog