[PATCH v6 10/12] mm/mempolicy: add get_mempolicy2 syscall

From: Gregory Price
Date: Wed Jan 03 2024 - 17:46:49 EST

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get_mempolicy2 is an extensible get_mempolicy interface which allows
a user to retrieve the memory policy for a task or address.

Defined as:

get_mempolicy2(struct mpol_param *param, size_t size,
unsigned long addr, unsigned long flags)

Top level input values:

mpol_param: The field which collects information about the mempolicy
returned to userspace.
addr: if MPOL_F_ADDR is passed in `flags`, this address will be
used to return the mempolicy details of the vma the
address belongs to
flags: if MPOL_F_ADDR, return mempolicy info vma containing addr
else, returns task mempolicy information

Input values include the following fields of mpol_param:

pol_maxnodes: if pol_nodes is set, must describe max number of nodes
to be copied to pol_nodes
pol_nodes: if set, the nodemask of the policy returned here

Output values include the following fields of mpol_param:

mode: mempolicy mode
mode_flags: mempolicy mode flags
home_node: policy home node will be returned here, or -1 if not.
pol_nodes: if set, the nodemask for the mempolicy

MPOL_F_NODE has been dropped from get_mempolicy2 (EINVAL).

MPOL_F_NODE originally allowed for either the ability to acquire
the node the page of `addr` is presently allocated on - or, if
addr is not provided and the policy mode is MPOL_INTERLEAVE - it
would return the node that would be used for the next allocation.

Neither of these capabilities were pulled forward into get_mempolicy2
a) both are still possible to acquire via get_mempolicy()
b) both of pieces of data are racey by definition and have not
proven useful.
c) Should such a use be identified, it can be easily added back
into mempolicy2 as an extension.

MPOL_F_MEMS_ALLOWED has been dropped from get_mempolicy2 (EINVAL).

MPOL_F_MEMS_ALLOWED originally returned the task->mems_allowed
nodemask in the nodemask parameter instead of the task or vma
nodemask.
a) this is still accessible from get_mempolicy()
b) task->mems_allowed is not technically part of mempolicy,
though it is related.
c) should this warrant bringing forward (in the scenario
where get_mempolicy is deprecated), it can be added as
an explicit extension. Or more smartly: implemented as
its own syscall.

Suggested-by: Michal Hocko <mhocko@xxxxxxxx>
Signed-off-by: Gregory Price <gregory.price@xxxxxxxxxxxx>
Acked-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
---
.../admin-guide/mm/numa_memory_policy.rst | 11 ++++-
arch/alpha/kernel/syscalls/syscall.tbl | 1 +
arch/arm/tools/syscall.tbl | 1 +
arch/arm64/include/asm/unistd.h | 2 +-
arch/arm64/include/asm/unistd32.h | 2 +
arch/m68k/kernel/syscalls/syscall.tbl | 1 +
arch/microblaze/kernel/syscalls/syscall.tbl | 1 +
arch/mips/kernel/syscalls/syscall_n32.tbl | 1 +
arch/mips/kernel/syscalls/syscall_o32.tbl | 1 +
arch/parisc/kernel/syscalls/syscall.tbl | 1 +
arch/powerpc/kernel/syscalls/syscall.tbl | 1 +
arch/s390/kernel/syscalls/syscall.tbl | 1 +
arch/sh/kernel/syscalls/syscall.tbl | 1 +
arch/sparc/kernel/syscalls/syscall.tbl | 1 +
arch/x86/entry/syscalls/syscall_32.tbl | 1 +
arch/x86/entry/syscalls/syscall_64.tbl | 1 +
arch/xtensa/kernel/syscalls/syscall.tbl | 1 +
include/linux/syscalls.h | 2 +
include/uapi/asm-generic/unistd.h | 4 +-
kernel/sys_ni.c | 1 +
mm/mempolicy.c | 42 +++++++++++++++++++
.../arch/mips/entry/syscalls/syscall_n64.tbl | 1 +
.../arch/powerpc/entry/syscalls/syscall.tbl | 1 +
.../perf/arch/s390/entry/syscalls/syscall.tbl | 1 +
.../arch/x86/entry/syscalls/syscall_64.tbl | 1 +
25 files changed, 79 insertions(+), 3 deletions(-)

diff --git a/Documentation/admin-guide/mm/numa_memory_policy.rst b/Documentation/admin-guide/mm/numa_memory_policy.rst
index 62a4ea14c646..a2ff6e89e48b 100644
--- a/Documentation/admin-guide/mm/numa_memory_policy.rst
+++ b/Documentation/admin-guide/mm/numa_memory_policy.rst
@@ -454,11 +454,20 @@ Get [Task] Memory Policy or Related Information::
long get_mempolicy(int *mode,
const unsigned long *nmask, unsigned long maxnode,
void *addr, int flags);
+ long get_mempolicy2(struct mpol_param *param, size_t size,
+ unsigned long addr, unsigned long flags);

Queries the "task/process memory policy" of the calling task, or the
policy or location of a specified virtual address, depending on the
'flags' argument.

+get_mempolicy2() is an extended version of get_mempolicy() capable of
+acquiring extended information about a mempolicy, including those
+that can only be set via set_mempolicy2() or mbind2().
+
+MPOL_F_NODE functionality has been removed from get_mempolicy2(),
+but can still be accessed via get_mempolicy().
+
See the get_mempolicy(2) man page for more details

@@ -501,7 +510,7 @@ Extended Mempolicy Arguments::
The extended mempolicy argument structure is defined to allow the mempolicy
interfaces future extensibility without the need for additional system calls.

-Extended interfaces (set_mempolicy2) use this argument structure.
+Extended interfaces (set_mempolicy2 and get_mempolicy2) use this structure.

The core arguments (mode, mode_flags, pol_nodes, and pol_maxnodes) apply to
all interfaces relative to their non-extended counterparts. Each additional
diff --git a/arch/alpha/kernel/syscalls/syscall.tbl b/arch/alpha/kernel/syscalls/syscall.tbl
index 0dc288a1118a..0301a8b0a262 100644
--- a/arch/alpha/kernel/syscalls/syscall.tbl
+++ b/arch/alpha/kernel/syscalls/syscall.tbl
@@ -497,3 +497,4 @@
565 common futex_wait sys_futex_wait
566 common futex_requeue sys_futex_requeue
567 common set_mempolicy2 sys_set_mempolicy2
+568 common get_mempolicy2 sys_get_mempolicy2
diff --git a/arch/arm/tools/syscall.tbl b/arch/arm/tools/syscall.tbl
index 50172ec0e1f5..771a33446e8e 100644
--- a/arch/arm/tools/syscall.tbl
+++ b/arch/arm/tools/syscall.tbl
@@ -471,3 +471,4 @@
455 common futex_wait sys_futex_wait
456 common futex_requeue sys_futex_requeue
457 common set_mempolicy2 sys_set_mempolicy2
+458 common get_mempolicy2 sys_get_mempolicy2
diff --git a/arch/arm64/include/asm/unistd.h b/arch/arm64/include/asm/unistd.h
index 298313d2e0af..b63f870debaf 100644
--- a/arch/arm64/include/asm/unistd.h
+++ b/arch/arm64/include/asm/unistd.h
@@ -39,7 +39,7 @@
#define __ARM_NR_compat_set_tls (__ARM_NR_COMPAT_BASE + 5)
#define __ARM_NR_COMPAT_END (__ARM_NR_COMPAT_BASE + 0x800)

-#define __NR_compat_syscalls 458
+#define __NR_compat_syscalls 459
#endif

#define __ARCH_WANT_SYS_CLONE
diff --git a/arch/arm64/include/asm/unistd32.h b/arch/arm64/include/asm/unistd32.h
index cee8d669c342..f8d01007aee0 100644
--- a/arch/arm64/include/asm/unistd32.h
+++ b/arch/arm64/include/asm/unistd32.h
@@ -921,6 +921,8 @@ __SYSCALL(__NR_futex_wait, sys_futex_wait)
__SYSCALL(__NR_futex_requeue, sys_futex_requeue)
#define __NR_set_mempolicy2 457
__SYSCALL(__NR_set_mempolicy2, sys_set_mempolicy2)
+#define __NR_get_mempolicy2 458
+__SYSCALL(__NR_get_mempolicy2, sys_get_mempolicy2)

/*
* Please add new compat syscalls above this comment and update
diff --git a/arch/m68k/kernel/syscalls/syscall.tbl b/arch/m68k/kernel/syscalls/syscall.tbl
index 839d90c535f2..048a409e684c 100644
--- a/arch/m68k/kernel/syscalls/syscall.tbl
+++ b/arch/m68k/kernel/syscalls/syscall.tbl
@@ -457,3 +457,4 @@
455 common futex_wait sys_futex_wait
456 common futex_requeue sys_futex_requeue
457 common set_mempolicy2 sys_set_mempolicy2
+458 common get_mempolicy2 sys_get_mempolicy2
diff --git a/arch/microblaze/kernel/syscalls/syscall.tbl b/arch/microblaze/kernel/syscalls/syscall.tbl
index 567c8b883735..327b01bd6793 100644
--- a/arch/microblaze/kernel/syscalls/syscall.tbl
+++ b/arch/microblaze/kernel/syscalls/syscall.tbl
@@ -463,3 +463,4 @@
455 common futex_wait sys_futex_wait
456 common futex_requeue sys_futex_requeue
457 common set_mempolicy2 sys_set_mempolicy2
+458 common get_mempolicy2 sys_get_mempolicy2
diff --git a/arch/mips/kernel/syscalls/syscall_n32.tbl b/arch/mips/kernel/syscalls/syscall_n32.tbl
index cc0640e16f2f..921d58e1da23 100644
--- a/arch/mips/kernel/syscalls/syscall_n32.tbl
+++ b/arch/mips/kernel/syscalls/syscall_n32.tbl
@@ -396,3 +396,4 @@
455 n32 futex_wait sys_futex_wait
456 n32 futex_requeue sys_futex_requeue
457 n32 set_mempolicy2 sys_set_mempolicy2
+458 n32 get_mempolicy2 sys_get_mempolicy2
diff --git a/arch/mips/kernel/syscalls/syscall_o32.tbl b/arch/mips/kernel/syscalls/syscall_o32.tbl
index f7262fde98d9..9271c83c9993 100644
--- a/arch/mips/kernel/syscalls/syscall_o32.tbl
+++ b/arch/mips/kernel/syscalls/syscall_o32.tbl
@@ -445,3 +445,4 @@
455 o32 futex_wait sys_futex_wait
456 o32 futex_requeue sys_futex_requeue
457 o32 set_mempolicy2 sys_set_mempolicy2
+458 o32 get_mempolicy2 sys_get_mempolicy2
diff --git a/arch/parisc/kernel/syscalls/syscall.tbl b/arch/parisc/kernel/syscalls/syscall.tbl
index e10f0e8bd064..0654f3f89fc7 100644
--- a/arch/parisc/kernel/syscalls/syscall.tbl
+++ b/arch/parisc/kernel/syscalls/syscall.tbl
@@ -456,3 +456,4 @@
455 common futex_wait sys_futex_wait
456 common futex_requeue sys_futex_requeue
457 common set_mempolicy2 sys_set_mempolicy2
+458 common get_mempolicy2 sys_get_mempolicy2
diff --git a/arch/powerpc/kernel/syscalls/syscall.tbl b/arch/powerpc/kernel/syscalls/syscall.tbl
index 4f03f5f42b78..ac11d2064e7a 100644
--- a/arch/powerpc/kernel/syscalls/syscall.tbl
+++ b/arch/powerpc/kernel/syscalls/syscall.tbl
@@ -544,3 +544,4 @@
455 common futex_wait sys_futex_wait
456 common futex_requeue sys_futex_requeue
457 common set_mempolicy2 sys_set_mempolicy2
+458 common get_mempolicy2 sys_get_mempolicy2
diff --git a/arch/s390/kernel/syscalls/syscall.tbl b/arch/s390/kernel/syscalls/syscall.tbl
index f98dadc2e9df..1cdcafe1ccca 100644
--- a/arch/s390/kernel/syscalls/syscall.tbl
+++ b/arch/s390/kernel/syscalls/syscall.tbl
@@ -460,3 +460,4 @@
455 common futex_wait sys_futex_wait sys_futex_wait
456 common futex_requeue sys_futex_requeue sys_futex_requeue
457 common set_mempolicy2 sys_set_mempolicy2 sys_set_mempolicy2
+458 common get_mempolicy2 sys_get_mempolicy2 sys_get_mempolicy2
diff --git a/arch/sh/kernel/syscalls/syscall.tbl b/arch/sh/kernel/syscalls/syscall.tbl
index f47ba9f2d05d..f71742024c29 100644
--- a/arch/sh/kernel/syscalls/syscall.tbl
+++ b/arch/sh/kernel/syscalls/syscall.tbl
@@ -460,3 +460,4 @@
455 common futex_wait sys_futex_wait
456 common futex_requeue sys_futex_requeue
457 common set_mempolicy2 sys_set_mempolicy2
+458 common get_mempolicy2 sys_get_mempolicy2
diff --git a/arch/sparc/kernel/syscalls/syscall.tbl b/arch/sparc/kernel/syscalls/syscall.tbl
index 53fb16616728..2fbf5dbe0620 100644
--- a/arch/sparc/kernel/syscalls/syscall.tbl
+++ b/arch/sparc/kernel/syscalls/syscall.tbl
@@ -503,3 +503,4 @@
455 common futex_wait sys_futex_wait
456 common futex_requeue sys_futex_requeue
457 common set_mempolicy2 sys_set_mempolicy2
+458 common get_mempolicy2 sys_get_mempolicy2
diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index 4b4dc41b24ee..0af813b9a118 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -462,3 +462,4 @@
455 i386 futex_wait sys_futex_wait
456 i386 futex_requeue sys_futex_requeue
457 i386 set_mempolicy2 sys_set_mempolicy2
+458 i386 get_mempolicy2 sys_get_mempolicy2
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index 1bc2190bec27..0b777876fc15 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -379,6 +379,7 @@
455 common futex_wait sys_futex_wait
456 common futex_requeue sys_futex_requeue
457 common set_mempolicy2 sys_set_mempolicy2
+458 common get_mempolicy2 sys_get_mempolicy2

#
# Due to a historical design error, certain syscalls are numbered differently
diff --git a/arch/xtensa/kernel/syscalls/syscall.tbl b/arch/xtensa/kernel/syscalls/syscall.tbl
index e26dc89399eb..4536c9a4227d 100644
--- a/arch/xtensa/kernel/syscalls/syscall.tbl
+++ b/arch/xtensa/kernel/syscalls/syscall.tbl
@@ -428,3 +428,4 @@
455 common futex_wait sys_futex_wait
456 common futex_requeue sys_futex_requeue
457 common set_mempolicy2 sys_set_mempolicy2
+458 common get_mempolicy2 sys_get_mempolicy2
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index b37ea6715456..c4dc5069bae7 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -821,6 +821,8 @@ asmlinkage long sys_get_mempolicy(int __user *policy,
unsigned long __user *nmask,
unsigned long maxnode,
unsigned long addr, unsigned long flags);
+asmlinkage long sys_get_mempolicy2(struct mpol_param __user *param, size_t size,
+ unsigned long addr, unsigned long flags);
asmlinkage long sys_set_mempolicy(int mode, const unsigned long __user *nmask,
unsigned long maxnode);
asmlinkage long sys_set_mempolicy2(struct mpol_param __user *param, size_t size,
diff --git a/include/uapi/asm-generic/unistd.h b/include/uapi/asm-generic/unistd.h
index 55486aba099f..719accc731db 100644
--- a/include/uapi/asm-generic/unistd.h
+++ b/include/uapi/asm-generic/unistd.h
@@ -830,9 +830,11 @@ __SYSCALL(__NR_futex_wait, sys_futex_wait)
__SYSCALL(__NR_futex_requeue, sys_futex_requeue)
#define __NR_set_mempolicy2 457
__SYSCALL(__NR_set_mempolicy2, sys_set_mempolicy2)
+#define __NR_get_mempolicy2 458
+__SYSCALL(__NR_get_mempolicy2, sys_get_mempolicy2)

#undef __NR_syscalls
-#define __NR_syscalls 458
+#define __NR_syscalls 459

/*
* 32 bit systems traditionally used different
diff --git a/kernel/sys_ni.c b/kernel/sys_ni.c
index fa1373c8bff8..6afbd3a41319 100644
--- a/kernel/sys_ni.c
+++ b/kernel/sys_ni.c
@@ -188,6 +188,7 @@ COND_SYSCALL(process_mrelease);
COND_SYSCALL(remap_file_pages);
COND_SYSCALL(mbind);
COND_SYSCALL(get_mempolicy);
+COND_SYSCALL(get_mempolicy2);
COND_SYSCALL(set_mempolicy);
COND_SYSCALL(set_mempolicy2);
COND_SYSCALL(migrate_pages);
diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index 84d877195deb..0b2e31d8636d 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1873,6 +1873,48 @@ SYSCALL_DEFINE5(get_mempolicy, int __user *, policy,
return kernel_get_mempolicy(policy, nmask, maxnode, addr, flags);
}

+SYSCALL_DEFINE4(get_mempolicy2, struct mpol_param __user *, uparam, size_t, usize,
+ unsigned long, addr, unsigned long, flags)
+{
+ struct mpol_param kparam;
+ struct mempolicy_param mparam;
+ int err;
+ nodemask_t policy_nodemask;
+ unsigned long __user *nodes_ptr;
+
+ if (flags & ~(MPOL_F_ADDR))
+ return -EINVAL;
+
+ /* initialize any memory liable to be copied to userland */
+ memset(&mparam, 0, sizeof(mparam));
+
+ err = copy_struct_from_user(&kparam, sizeof(kparam), uparam, usize);
+ if (err)
+ return -EINVAL;
+
+ mparam.policy_nodes = kparam.pol_nodes ? &policy_nodemask : NULL;
+ if (flags & MPOL_F_ADDR)
+ err = do_get_vma_mempolicy(untagged_addr(addr), NULL, &mparam);
+ else
+ err = do_get_task_mempolicy(&mparam, NULL);
+
+ if (err)
+ return err;
+
+ kparam.mode = mparam.mode;
+ kparam.mode_flags = mparam.mode_flags;
+ kparam.home_node = mparam.home_node;
+ if (kparam.pol_nodes) {
+ nodes_ptr = u64_to_user_ptr(kparam.pol_nodes);
+ err = copy_nodes_to_user(nodes_ptr, kparam.pol_maxnodes,
+ mparam.policy_nodes);
+ if (err)
+ return err;
+ }
+
+ return copy_to_user(uparam, &kparam, usize) ? -EFAULT : 0;
+}
+
bool vma_migratable(struct vm_area_struct *vma)
{
if (vma->vm_flags & (VM_IO | VM_PFNMAP))
diff --git a/tools/perf/arch/mips/entry/syscalls/syscall_n64.tbl b/tools/perf/arch/mips/entry/syscalls/syscall_n64.tbl
index bb1351df51d9..c34c6877379e 100644
--- a/tools/perf/arch/mips/entry/syscalls/syscall_n64.tbl
+++ b/tools/perf/arch/mips/entry/syscalls/syscall_n64.tbl
@@ -372,3 +372,4 @@
455 n64 futex_wait sys_futex_wait
456 n64 futex_requeue sys_futex_requeue
457 n64 set_mempolicy2 sys_set_mempolicy2
+458 n64 get_mempolicy2 sys_get_mempolicy2
diff --git a/tools/perf/arch/powerpc/entry/syscalls/syscall.tbl b/tools/perf/arch/powerpc/entry/syscalls/syscall.tbl
index 4f03f5f42b78..ac11d2064e7a 100644
--- a/tools/perf/arch/powerpc/entry/syscalls/syscall.tbl
+++ b/tools/perf/arch/powerpc/entry/syscalls/syscall.tbl
@@ -544,3 +544,4 @@
455 common futex_wait sys_futex_wait
456 common futex_requeue sys_futex_requeue
457 common set_mempolicy2 sys_set_mempolicy2
+458 common get_mempolicy2 sys_get_mempolicy2
diff --git a/tools/perf/arch/s390/entry/syscalls/syscall.tbl b/tools/perf/arch/s390/entry/syscalls/syscall.tbl
index f98dadc2e9df..1cdcafe1ccca 100644
--- a/tools/perf/arch/s390/entry/syscalls/syscall.tbl
+++ b/tools/perf/arch/s390/entry/syscalls/syscall.tbl
@@ -460,3 +460,4 @@
455 common futex_wait sys_futex_wait sys_futex_wait
456 common futex_requeue sys_futex_requeue sys_futex_requeue
457 common set_mempolicy2 sys_set_mempolicy2 sys_set_mempolicy2
+458 common get_mempolicy2 sys_get_mempolicy2 sys_get_mempolicy2
diff --git a/tools/perf/arch/x86/entry/syscalls/syscall_64.tbl b/tools/perf/arch/x86/entry/syscalls/syscall_64.tbl
index 21f2579679d4..edf338f32645 100644
--- a/tools/perf/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/tools/perf/arch/x86/entry/syscalls/syscall_64.tbl
@@ -379,6 +379,7 @@
455 common futex_wait sys_futex_wait
456 common futex_requeue sys_futex_requeue
457 common set_mempolicy2 sys_set_mempolicy2
+458 common get_mempolicy2 sys_get_mempolicy2

#
# Due to a historical design error, certain syscalls are numbered differently
--
2.39.1

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