Message-ID: <20110719003537.16b189ae@lilo>
Date:	Tue, 19 Jul 2011 00:35:37 +0930
From:	Christopher Yeoh <cyeoh@....ibm.com>
To:	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org
Cc:	linux-kernel@...r.kernel.org, linux-man@...r.kernel.org,
	linux-arch@...r.kernel.org
Subject: Cross Memory Attach v3

Hi Andrew,

Resending with CC's as you requested. Have added information about a man
page and what is required for arches other than x86 and powerpc which
have already been done.

Just as a reminder of what has happened so far, repeating some content
from previous emails about it:

The basic idea behind cross memory attach is to allow MPI programs doing
intra-node communication to do a single copy of the message rather than
a double copy of the message via shared memory.

The following patch attempts to achieve this by allowing a
destination process, given an address and size from a source process, to
copy memory directly from the source process into its own address space
via a system call. There is also a symmetrical ability to copy from 
the current process's address space into a destination process's
address space.

- Use of /proc/pid/mem has been considered, but there are issues with 
  using it:
  - Does not allow for specifying iovecs for both src and dest, assuming
    preadv or pwritev was implemented either the area read from or
  written to would need to be contiguous. 
  - Currently mem_read allows only processes who are currently
  ptrace'ing the target and are still able to ptrace the target to read
  from the target. This check could possibly be moved to the open call,
  but its not clear exactly what race this restriction is stopping
  (reason  appears to have been lost)
  - Having to send the fd of /proc/self/mem via SCM_RIGHTS on unix
  domain socket is a bit ugly from a userspace point of view,
  especially when you may have hundreds if not (eventually) thousands
  of processes  that all need to do this with each other
  - Doesn't allow for some future use of the interface we would like to
  consider adding in the future (see below)
  - Interestingly reading from /proc/pid/mem currently actually
  involves two copies! (But this could be fixed pretty easily)

As mentioned previously use of vmsplice instead was considered, 
but has problems. Since you need the reader and writer working
co-operatively if the pipe is not drained then you block. Which
requires some wrapping to do non blocking on the send side or polling
on the receive. In all to all communication it requires ordering
otherwise you can deadlock. And in the example of many MPI tasks
writing to one MPI task vmsplice serialises the copying.

There are some cases of MPI collectives where even a single copy
interface does not get us the performance gain we could. For example in
an MPI_Reduce rather than copy the data from the source we would like
to instead use it directly in a mathops (say the reduce is doing a sum)
as this would save us doing a copy. We don't need to keep a copy of the
data from the source. I haven't implemented this, but I think this
interface could in the future do all this through the use of the flags
- eg could specify the math operation and type and the kernel rather
than just copying the data would apply the specified operation between
the source and destination and store it in the destination. 

Although we don't have a "second user" of the interface (though I've
had some nibbles from people who may be interested in using it for
intra process messaging which is not MPI). This interface is something
which hardware vendors are already doing for their custom drivers to
implement fast local communication. And so in addition to this being
useful for OpenMPI it would mean the driver maintainers don't have to
fix things up when the mm changes. 

There was some discussion about how much faster a true zero copy would
go. Here's a link back to the email with some testing I did on that:

http://marc.info/?l=linux-mm&m=130105930902915&w=2

There is a basic man page for the proposed interface here:

http://ozlabs.org/~cyeoh/cma/process_vm_readv.txt

This has been implemented for x86 and powerpc, other architecture should
mainly (I think) just need to add syscall numbers for the process_vm_readv
and process_vm_writev. There are 32 bit compatibility versions for
64-bit kernels.

For arch maintainers there are some simple tests to be able to quickly 
verify that the syscalls are working correctly here:

http://ozlabs.org/~cyeoh/cma/cma-test-20110718.tgz

Regards,

Chris
-- 
cyeoh@...ibm.com
Signed-off-by: Chris Yeoh <yeohc@....ibm.com>
---
 arch/powerpc/include/asm/systbl.h  |    2 
 arch/powerpc/include/asm/unistd.h  |    4 
 arch/x86/include/asm/unistd_32.h   |    4 
 arch/x86/kernel/syscall_table_32.S |    2 
 fs/aio.c                           |    4 
 fs/compat.c                        |    7 
 fs/read_write.c                    |    8 
 include/linux/compat.h             |    3 
 include/linux/fs.h                 |    7 
 include/linux/syscalls.h           |   13 +
 mm/Makefile                        |    3 
 mm/process_vm_access.c             |  446 +++++++++++++++++++++++++++++++++++++
 security/keys/compat.c             |    2 
 security/keys/keyctl.c             |    2 
 14 files changed, 490 insertions(+), 17 deletions(-)

diff --git a/arch/powerpc/include/asm/systbl.h b/arch/powerpc/include/asm/systbl.h
index f6736b7..525db4b 100644
--- a/arch/powerpc/include/asm/systbl.h
+++ b/arch/powerpc/include/asm/systbl.h
@@ -354,3 +354,5 @@ COMPAT_SYS_SPU(clock_adjtime)
 SYSCALL_SPU(syncfs)
 COMPAT_SYS_SPU(sendmmsg)
 SYSCALL_SPU(setns)
+COMPAT_SYS(process_vm_readv)
+COMPAT_SYS(process_vm_writev)
diff --git a/arch/powerpc/include/asm/unistd.h b/arch/powerpc/include/asm/unistd.h
index b8b3f59..d3d1b5e 100644
--- a/arch/powerpc/include/asm/unistd.h
+++ b/arch/powerpc/include/asm/unistd.h
@@ -373,10 +373,12 @@
 #define __NR_syncfs		348
 #define __NR_sendmmsg		349
 #define __NR_setns		350
+#define __NR_process_vm_readv	351
+#define __NR_process_vm_writev	352
 
 #ifdef __KERNEL__
 
-#define __NR_syscalls		351
+#define __NR_syscalls		353
 
 #define __NR__exit __NR_exit
 #define NR_syscalls	__NR_syscalls
diff --git a/arch/x86/include/asm/unistd_32.h b/arch/x86/include/asm/unistd_32.h
index 593485b..599c77d 100644
--- a/arch/x86/include/asm/unistd_32.h
+++ b/arch/x86/include/asm/unistd_32.h
@@ -352,10 +352,12 @@
 #define __NR_syncfs             344
 #define __NR_sendmmsg		345
 #define __NR_setns		346
+#define __NR_process_vm_readv	347
+#define __NR_process_vm_writev	348
 
 #ifdef __KERNEL__
 
-#define NR_syscalls 347
+#define NR_syscalls 349
 
 #define __ARCH_WANT_IPC_PARSE_VERSION
 #define __ARCH_WANT_OLD_READDIR
diff --git a/arch/x86/kernel/syscall_table_32.S b/arch/x86/kernel/syscall_table_32.S
index fbb0a04..ca0fe4d 100644
--- a/arch/x86/kernel/syscall_table_32.S
+++ b/arch/x86/kernel/syscall_table_32.S
@@ -346,3 +346,5 @@ ENTRY(sys_call_table)
 	.long sys_syncfs
 	.long sys_sendmmsg		/* 345 */
 	.long sys_setns
+	.long sys_process_vm_readv
+	.long sys_process_vm_writev
diff --git a/fs/aio.c b/fs/aio.c
index e29ec48..632b235 100644
--- a/fs/aio.c
+++ b/fs/aio.c
@@ -1387,13 +1387,13 @@ static ssize_t aio_setup_vectored_rw(int type, struct kiocb *kiocb, bool compat)
 		ret = compat_rw_copy_check_uvector(type,
 				(struct compat_iovec __user *)kiocb->ki_buf,
 				kiocb->ki_nbytes, 1, &kiocb->ki_inline_vec,
-				&kiocb->ki_iovec);
+				&kiocb->ki_iovec, 1);
 	else
 #endif
 		ret = rw_copy_check_uvector(type,
 				(struct iovec __user *)kiocb->ki_buf,
 				kiocb->ki_nbytes, 1, &kiocb->ki_inline_vec,
-				&kiocb->ki_iovec);
+				&kiocb->ki_iovec, 1);
 	if (ret < 0)
 		goto out;
 
diff --git a/fs/compat.c b/fs/compat.c
index 0ea0083..ec53ccc 100644
--- a/fs/compat.c
+++ b/fs/compat.c
@@ -550,7 +550,7 @@ out:
 ssize_t compat_rw_copy_check_uvector(int type,
 		const struct compat_iovec __user *uvector, unsigned long nr_segs,
 		unsigned long fast_segs, struct iovec *fast_pointer,
-		struct iovec **ret_pointer)
+		struct iovec **ret_pointer, int check_access)
 {
 	compat_ssize_t tot_len;
 	struct iovec *iov = *ret_pointer = fast_pointer;
@@ -597,7 +597,8 @@ ssize_t compat_rw_copy_check_uvector(int type,
 		}
 		if (len < 0)	/* size_t not fitting in compat_ssize_t .. */
 			goto out;
-		if (!access_ok(vrfy_dir(type), compat_ptr(buf), len)) {
+		if (check_access &&
+		    !access_ok(vrfy_dir(type), compat_ptr(buf), len)) {
 			ret = -EFAULT;
 			goto out;
 		}
@@ -1111,7 +1112,7 @@ static ssize_t compat_do_readv_writev(int type, struct file *file,
 		goto out;
 
 	tot_len = compat_rw_copy_check_uvector(type, uvector, nr_segs,
-					       UIO_FASTIOV, iovstack, &iov);
+					       UIO_FASTIOV, iovstack, &iov, 1);
 	if (tot_len == 0) {
 		ret = 0;
 		goto out;
diff --git a/fs/read_write.c b/fs/read_write.c
index 5520f8a..b905826 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -575,7 +575,8 @@ ssize_t do_loop_readv_writev(struct file *filp, struct iovec *iov,
 ssize_t rw_copy_check_uvector(int type, const struct iovec __user * uvector,
 			      unsigned long nr_segs, unsigned long fast_segs,
 			      struct iovec *fast_pointer,
-			      struct iovec **ret_pointer)
+			      struct iovec **ret_pointer,
+			      int check_access)
 {
 	unsigned long seg;
 	ssize_t ret;
@@ -631,7 +632,8 @@ ssize_t rw_copy_check_uvector(int type, const struct iovec __user * uvector,
 			ret = -EINVAL;
 			goto out;
 		}
-		if (unlikely(!access_ok(vrfy_dir(type), buf, len))) {
+		if (check_access
+		    && unlikely(!access_ok(vrfy_dir(type), buf, len))) {
 			ret = -EFAULT;
 			goto out;
 		}
@@ -663,7 +665,7 @@ static ssize_t do_readv_writev(int type, struct file *file,
 	}
 
 	ret = rw_copy_check_uvector(type, uvector, nr_segs,
-			ARRAY_SIZE(iovstack), iovstack, &iov);
+				    ARRAY_SIZE(iovstack), iovstack, &iov, 1);
 	if (ret <= 0)
 		goto out;
 
diff --git a/include/linux/compat.h b/include/linux/compat.h
index 846bb17..1cc917a 100644
--- a/include/linux/compat.h
+++ b/include/linux/compat.h
@@ -557,7 +557,8 @@ extern ssize_t compat_rw_copy_check_uvector(int type,
 		const struct compat_iovec __user *uvector,
 		unsigned long nr_segs,
 		unsigned long fast_segs, struct iovec *fast_pointer,
-		struct iovec **ret_pointer);
+		struct iovec **ret_pointer,
+		int check_access);
 
 extern void __user *compat_alloc_user_space(unsigned long len);
 
diff --git a/include/linux/fs.h b/include/linux/fs.h
index b5b9792..d97ffab 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -1608,9 +1608,10 @@ struct inode_operations {
 struct seq_file;
 
 ssize_t rw_copy_check_uvector(int type, const struct iovec __user * uvector,
-				unsigned long nr_segs, unsigned long fast_segs,
-				struct iovec *fast_pointer,
-				struct iovec **ret_pointer);
+			      unsigned long nr_segs, unsigned long fast_segs,
+			      struct iovec *fast_pointer,
+			      struct iovec **ret_pointer,
+			      int check_access);
 
 extern ssize_t vfs_read(struct file *, char __user *, size_t, loff_t *);
 extern ssize_t vfs_write(struct file *, const char __user *, size_t, loff_t *);
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 8c03b98..0dc0809 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -847,4 +847,17 @@ asmlinkage long sys_open_by_handle_at(int mountdirfd,
 				      struct file_handle __user *handle,
 				      int flags);
 asmlinkage long sys_setns(int fd, int nstype);
+asmlinkage long sys_process_vm_readv(pid_t pid,
+				     const struct iovec __user *lvec,
+				     unsigned long liovcnt,
+				     const struct iovec __user *rvec,
+				     unsigned long riovcnt,
+				     unsigned long flags);
+asmlinkage long sys_process_vm_writev(pid_t pid,
+				      const struct iovec __user *lvec,
+				      unsigned long liovcnt,
+				      const struct iovec __user *rvec,
+				      unsigned long riovcnt,
+				      unsigned long flags);
+
 #endif
diff --git a/mm/Makefile b/mm/Makefile
index 836e416..50ec00e 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -5,7 +5,8 @@
 mmu-y			:= nommu.o
 mmu-$(CONFIG_MMU)	:= fremap.o highmem.o madvise.o memory.o mincore.o \
 			   mlock.o mmap.o mprotect.o mremap.o msync.o rmap.o \
-			   vmalloc.o pagewalk.o pgtable-generic.o
+			   vmalloc.o pagewalk.o pgtable-generic.o \
+			   process_vm_access.o
 
 obj-y			:= filemap.o mempool.o oom_kill.o fadvise.o \
 			   maccess.o page_alloc.o page-writeback.o \
diff --git a/mm/process_vm_access.c b/mm/process_vm_access.c
new file mode 100644
index 0000000..0df7696
--- /dev/null
+++ b/mm/process_vm_access.c
@@ -0,0 +1,446 @@
+/*
+ *  linux/mm/process_vm_access.c
+ *
+ *  Copyright (C) 2010-2011 Christopher Yeoh <cyeoh@....ibm.com>, IBM Corp.
+ */
+
+#include <linux/mm.h>
+#include <linux/uio.h>
+#include <linux/sched.h>
+#include <linux/highmem.h>
+#include <linux/ptrace.h>
+#include <linux/slab.h>
+#include <linux/syscalls.h>
+
+#ifdef CONFIG_COMPAT
+#include <linux/compat.h>
+#endif
+
+/*
+ * process_vm_rw_pages - read/write pages from task specified
+ * @task: task to read/write from
+ * @mm: mm for task
+ * @process_pages: struct pages area that can store at least
+ *  nr_pages_to_copy struct page pointers
+ * @pa: address of page in task to start copying from/to
+ * @start_offset: offset in page to start copying from/to
+ * @len: number of bytes to copy
+ * @lvec: iovec array specifying where to copy to/from
+ * @lvec_cnt: number of elements in iovec array
+ * @lvec_current: index in iovec array we are up to
+ * @lvec_offset: offset in bytes from current iovec iov_base we are up to
+ * @vm_write: 0 means copy from, 1 means copy to
+ * @nr_pages_to_copy: number of pages to copy
+ */
+static ssize_t process_vm_rw_pages(struct task_struct *task,
+				   struct mm_struct *mm,
+				   struct page **process_pages,
+				   unsigned long pa,
+				   unsigned long start_offset,
+				   unsigned long len,
+				   const struct iovec *lvec,
+				   unsigned long lvec_cnt,
+				   unsigned long *lvec_current,
+				   size_t *lvec_offset,
+				   int vm_write,
+				   unsigned int nr_pages_to_copy)
+{
+	int pages_pinned;
+	void *target_kaddr;
+	int pgs_copied = 0;
+	int j;
+	int ret;
+	ssize_t bytes_to_copy;
+	ssize_t bytes_copied = 0;
+	ssize_t rc = -EFAULT;
+
+	/* Get the pages we're interested in */
+	down_read(&mm->mmap_sem);
+	pages_pinned = get_user_pages(task, mm, pa,
+				      nr_pages_to_copy,
+				      vm_write, 0, process_pages, NULL);
+	up_read(&mm->mmap_sem);
+
+	if (pages_pinned != nr_pages_to_copy)
+		goto end;
+
+	/* Do the copy for each page */
+	for (pgs_copied = 0;
+	     (pgs_copied < nr_pages_to_copy) && (*lvec_current < lvec_cnt);
+	     pgs_copied++) {
+		/* Make sure we have a non zero length iovec */
+		while (*lvec_current < lvec_cnt
+		       && lvec[*lvec_current].iov_len == 0)
+			(*lvec_current)++;
+		if (*lvec_current == lvec_cnt)
+			break;
+
+		/*
+		 * Will copy smallest of:
+		 * - bytes remaining in page
+		 * - bytes remaining in destination iovec
+		 */
+		bytes_to_copy = min_t(ssize_t, PAGE_SIZE - start_offset,
+				      len - bytes_copied);
+		bytes_to_copy = min_t(ssize_t, bytes_to_copy,
+				      lvec[*lvec_current].iov_len
+				      - *lvec_offset);
+
+		target_kaddr = kmap(process_pages[pgs_copied]) + start_offset;
+
+		if (vm_write)
+			ret = copy_from_user(target_kaddr,
+					     lvec[*lvec_current].iov_base
+					     + *lvec_offset,
+					     bytes_to_copy);
+		else
+			ret = copy_to_user(lvec[*lvec_current].iov_base
+					   + *lvec_offset,
+					   target_kaddr, bytes_to_copy);
+		kunmap(process_pages[pgs_copied]);
+		if (ret) {
+			pgs_copied++;
+			goto end;
+		}
+		bytes_copied += bytes_to_copy;
+		*lvec_offset += bytes_to_copy;
+		if (*lvec_offset == lvec[*lvec_current].iov_len) {
+			/*
+			 * Need to copy remaining part of page into the
+			 * next iovec if there are any bytes left in page
+			 */
+			(*lvec_current)++;
+			*lvec_offset = 0;
+			start_offset = (start_offset + bytes_to_copy)
+				% PAGE_SIZE;
+			if (start_offset)
+				pgs_copied--;
+		} else {
+			start_offset = 0;
+		}
+	}
+
+	rc = bytes_copied;
+
+end:
+	if (vm_write) {
+		for (j = 0; j < pages_pinned; j++) {
+			if (j < pgs_copied)
+				set_page_dirty_lock(process_pages[j]);
+			put_page(process_pages[j]);
+		}
+	} else {
+		for (j = 0; j < pages_pinned; j++)
+			put_page(process_pages[j]);
+	}
+
+	return rc;
+}
+
+/* Maximum number of pages kmalloc'd to hold struct page's during copy */
+#define PVM_MAX_KMALLOC_PAGES (PAGE_SIZE * 2)
+
+/*
+ * process_vm_rw_single_vec - read/write pages from task specified
+ * @addr: start memory address of target process
+ * @len: size of area to copy to/from
+ * @lvec: iovec array specifying where to copy to/from locally
+ * @lvec_cnt: number of elements in iovec array
+ * @lvec_current: index in iovec array we are up to
+ * @lvec_offset: offset in bytes from current iovec iov_base we are up to
+ * @process_pages: struct pages area that can store at least
+ *  nr_pages_to_copy struct page pointers
+ * @mm: mm for task
+ * @task: task to read/write from
+ * @vm_write: 0 means copy from, 1 means copy to
+ */
+static ssize_t process_vm_rw_single_vec(unsigned long addr,
+					unsigned long len,
+					const struct iovec *lvec,
+					unsigned long lvec_cnt,
+					unsigned long *lvec_current,
+					size_t *lvec_offset,
+					struct page **process_pages,
+					struct mm_struct *mm,
+					struct task_struct *task,
+					int vm_write)
+{
+	unsigned long pa = addr & PAGE_MASK;
+	unsigned long start_offset = addr - pa;
+	unsigned long nr_pages;
+	ssize_t bytes_copied = 0;
+	ssize_t rc;
+	unsigned long nr_pages_copied = 0;
+	unsigned long nr_pages_to_copy;
+	unsigned long max_pages_per_loop = PVM_MAX_KMALLOC_PAGES
+		/ sizeof(struct pages *);
+
+
+	/* Work out address and page range required */
+	if (len == 0)
+		return 0;
+	nr_pages = (addr + len - 1) / PAGE_SIZE - addr / PAGE_SIZE + 1;
+
+
+	while ((nr_pages_copied < nr_pages) && (*lvec_current < lvec_cnt)) {
+		nr_pages_to_copy = min(nr_pages - nr_pages_copied,
+				       max_pages_per_loop);
+
+		rc = process_vm_rw_pages(task, mm, process_pages, pa,
+					 start_offset, len,
+					 lvec, lvec_cnt,
+					 lvec_current, lvec_offset,
+					 vm_write, nr_pages_to_copy);
+		start_offset = 0;
+
+		if (rc < 0)
+			return rc;
+		else {
+			bytes_copied += rc;
+			len -= rc;
+			nr_pages_copied += nr_pages_to_copy;
+			pa += nr_pages_to_copy * PAGE_SIZE;
+		}
+	}
+
+	rc = bytes_copied;
+	return rc;
+}
+
+static ssize_t process_vm_rw(pid_t pid, const struct iovec *lvec,
+			     unsigned long liovcnt,
+			     const struct iovec *rvec,
+			     unsigned long riovcnt,
+			     unsigned long flags, int vm_write)
+{
+	struct task_struct *task;
+	struct page **process_pages = NULL;
+	struct mm_struct *mm;
+	unsigned long i;
+	ssize_t rc;
+	ssize_t bytes_copied;
+	unsigned long nr_pages = 0;
+	unsigned long nr_pages_iov;
+	unsigned long iov_l_curr_idx = 0;
+	size_t iov_l_curr_offset = 0;
+	ssize_t iov_len;
+
+	/*
+	 * Work out how many pages of struct pages we're going to need
+	 * when eventually calling get_user_pages
+	 */
+	for (i = 0; i < riovcnt; i++) {
+		iov_len = rvec[i].iov_len;
+		if (iov_len > 0) {
+			nr_pages_iov = ((unsigned long)rvec[i].iov_base
+					+ iov_len)
+				/ PAGE_SIZE - (unsigned long)rvec[i].iov_base
+				/ PAGE_SIZE + 1;
+			nr_pages = max(nr_pages, nr_pages_iov);
+		}
+	}
+
+	if (nr_pages == 0)
+		return 0;
+
+	/* For reliability don't try to kmalloc more than 2 pages worth */
+	process_pages = kmalloc(min_t(size_t, PVM_MAX_KMALLOC_PAGES,
+				      sizeof(struct pages *)*nr_pages),
+				GFP_KERNEL);
+
+	if (!process_pages)
+		return -ENOMEM;
+
+	/* Get process information */
+	rcu_read_lock();
+	task = find_task_by_vpid(pid);
+	if (task)
+		get_task_struct(task);
+	rcu_read_unlock();
+	if (!task) {
+		rc = -ESRCH;
+		goto free_proc_pages;
+	}
+
+	task_lock(task);
+	if (__ptrace_may_access(task, PTRACE_MODE_ATTACH)) {
+		task_unlock(task);
+		rc = -EPERM;
+		goto put_task_struct;
+	}
+	mm = task->mm;
+
+	if (!mm || (task->flags & PF_KTHREAD)) {
+		task_unlock(task);
+		rc = -EINVAL;
+		goto put_task_struct;
+	}
+
+	atomic_inc(&mm->mm_users);
+	task_unlock(task);
+
+	rc = 0;
+	for (i = 0; i < riovcnt && iov_l_curr_idx < liovcnt; i++) {
+		bytes_copied = process_vm_rw_single_vec(
+			(unsigned long)rvec[i].iov_base, rvec[i].iov_len,
+			lvec, liovcnt, &iov_l_curr_idx, &iov_l_curr_offset,
+			process_pages, mm, task, vm_write);
+		if (bytes_copied < 0) {
+			rc = bytes_copied;
+			goto put_mm;
+		} else {
+			rc += bytes_copied;
+		}
+	}
+
+put_mm:
+	mmput(mm);
+
+put_task_struct:
+	put_task_struct(task);
+
+
+free_proc_pages:
+	kfree(process_pages);
+	return rc;
+}
+
+static ssize_t process_vm_rw_check_iovecs(pid_t pid,
+					  const struct iovec __user *lvec,
+					  unsigned long liovcnt,
+					  const struct iovec __user *rvec,
+					  unsigned long riovcnt,
+					  unsigned long flags, int vm_write)
+{
+	struct iovec iovstack_l[UIO_FASTIOV];
+	struct iovec iovstack_r[UIO_FASTIOV];
+	struct iovec *iov_l = iovstack_l;
+	struct iovec *iov_r = iovstack_r;
+	ssize_t rc;
+
+	if (flags != 0)
+		return -EINVAL;
+
+	/* Check iovecs */
+	if (vm_write)
+		rc = rw_copy_check_uvector(WRITE, lvec, liovcnt, UIO_FASTIOV,
+					   iovstack_l, &iov_l, 1);
+	else
+		rc = rw_copy_check_uvector(READ, lvec, liovcnt, UIO_FASTIOV,
+					   iovstack_l, &iov_l, 1);
+	if (rc <= 0)
+		goto free_iovecs;
+
+	rc = rw_copy_check_uvector(READ, rvec, riovcnt, UIO_FASTIOV,
+				   iovstack_r, &iov_r, 0);
+	if (rc <= 0)
+		goto free_iovecs;
+
+	rc = process_vm_rw(pid, iov_l, liovcnt, iov_r, riovcnt, flags,
+			    vm_write);
+
+free_iovecs:
+	if (iov_r != iovstack_r)
+		kfree(iov_r);
+	if (iov_l != iovstack_l)
+		kfree(iov_l);
+
+	return rc;
+}
+
+SYSCALL_DEFINE6(process_vm_readv, pid_t, pid, const struct iovec __user *, lvec,
+		unsigned long, liovcnt, const struct iovec __user *, rvec,
+		unsigned long, riovcnt,	unsigned long, flags)
+{
+	return process_vm_rw_check_iovecs(pid, lvec, liovcnt, rvec, riovcnt,
+					  flags, 0);
+}
+
+SYSCALL_DEFINE6(process_vm_writev, pid_t, pid,
+		const struct iovec __user *, lvec,
+		unsigned long, liovcnt, const struct iovec __user *, rvec,
+		unsigned long, riovcnt,	unsigned long, flags)
+{
+	return process_vm_rw_check_iovecs(pid, lvec, liovcnt, rvec, riovcnt,
+					  flags, 1);
+}
+
+#ifdef CONFIG_COMPAT
+
+asmlinkage ssize_t
+compat_process_vm_rw_check_iovecs(compat_pid_t pid,
+				  const struct compat_iovec __user *lvec,
+				  unsigned long liovcnt,
+				  const struct compat_iovec __user *rvec,
+				  unsigned long riovcnt,
+				  unsigned long flags, int vm_write)
+{
+	struct iovec iovstack_l[UIO_FASTIOV];
+	struct iovec iovstack_r[UIO_FASTIOV];
+	struct iovec *iov_l = iovstack_l;
+	struct iovec *iov_r = iovstack_r;
+	ssize_t rc = -EFAULT;
+
+	if (flags != 0)
+		return -EINVAL;
+
+	if (!access_ok(VERIFY_READ, lvec, liovcnt * sizeof(*lvec)))
+		goto out;
+
+	if (!access_ok(VERIFY_READ, rvec, riovcnt * sizeof(*rvec)))
+		goto out;
+
+	if (vm_write)
+		rc = compat_rw_copy_check_uvector(WRITE, lvec, liovcnt,
+						  UIO_FASTIOV, iovstack_l,
+						  &iov_l, 1);
+	else
+		rc = compat_rw_copy_check_uvector(READ, lvec, liovcnt,
+						  UIO_FASTIOV, iovstack_l,
+						  &iov_l, 1);
+	if (rc <= 0)
+		goto free_iovecs;
+	rc = compat_rw_copy_check_uvector(READ, rvec, riovcnt,
+					  UIO_FASTIOV, iovstack_r,
+					  &iov_r, 0);
+	if (rc <= 0)
+		goto free_iovecs;
+
+	rc = process_vm_rw(pid, iov_l, liovcnt, iov_r, riovcnt, flags,
+			    vm_write);
+
+free_iovecs:
+	if (iov_r != iovstack_r)
+		kfree(iov_r);
+	if (iov_l != iovstack_l)
+		kfree(iov_l);
+
+out:
+	return rc;
+}
+
+asmlinkage ssize_t
+compat_sys_process_vm_readv(compat_pid_t pid,
+			    const struct compat_iovec __user *lvec,
+			    unsigned long liovcnt,
+			    const struct compat_iovec __user *rvec,
+			    unsigned long riovcnt,
+			    unsigned long flags)
+{
+	return compat_process_vm_rw_check_iovecs(pid, lvec, liovcnt, rvec,
+						 riovcnt, flags, 0);
+}
+
+asmlinkage ssize_t
+compat_sys_process_vm_writev(compat_pid_t pid,
+			     const struct compat_iovec __user *lvec,
+			     unsigned long liovcnt,
+			     const struct compat_iovec __user *rvec,
+			     unsigned long riovcnt,
+			     unsigned long flags)
+{
+	return compat_process_vm_rw_check_iovecs(pid, lvec, liovcnt, rvec,
+						 riovcnt, flags, 1);
+}
+
+#endif
diff --git a/security/keys/compat.c b/security/keys/compat.c
index 338b510..4c48e13 100644
--- a/security/keys/compat.c
+++ b/security/keys/compat.c
@@ -38,7 +38,7 @@ long compat_keyctl_instantiate_key_iov(
 
 	ret = compat_rw_copy_check_uvector(WRITE, _payload_iov, ioc,
 					   ARRAY_SIZE(iovstack),
-					   iovstack, &iov);
+					   iovstack, &iov, 1);
 	if (ret < 0)
 		return ret;
 	if (ret == 0)
diff --git a/security/keys/keyctl.c b/security/keys/keyctl.c
index eca5191..0b3f5d7 100644
--- a/security/keys/keyctl.c
+++ b/security/keys/keyctl.c
@@ -1065,7 +1065,7 @@ long keyctl_instantiate_key_iov(key_serial_t id,
 		goto no_payload;
 
 	ret = rw_copy_check_uvector(WRITE, _payload_iov, ioc,
-				    ARRAY_SIZE(iovstack), iovstack, &iov);
+				    ARRAY_SIZE(iovstack), iovstack, &iov, 1);
 	if (ret < 0)
 		return ret;
 	if (ret == 0)
--
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