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userfaultfd: wp: add the writeprotect API to userfaultfd ioctl

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Introduce the new uffd-wp APIs for userspace.

Firstly, we'll allow to do UFFDIO_REGISTER with write protection tracking
using the new UFFDIO_REGISTER_MODE_WP flag.  Note that this flag can
co-exist with the existing UFFDIO_REGISTER_MODE_MISSING, in which case the
userspace program can not only resolve missing page faults, and at the
same time tracking page data changes along the way.

Secondly, we introduced the new UFFDIO_WRITEPROTECT API to do page level
write protection tracking.  Note that we will need to register the memory
region with UFFDIO_REGISTER_MODE_WP before that.

[peterx@redhat.com: write up the commit message]
[peterx@redhat.com: remove useless block, write commit message, check against
 VM_MAYWRITE rather than VM_WRITE when register]
Signed-off-by: Andrea Arcangeli <aarcange@redhat.com>
Signed-off-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Jerome Glisse <jglisse@redhat.com>
Cc: Bobby Powers <bobbypowers@gmail.com>
Cc: Brian Geffon <bgeffon@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Denis Plotnikov <dplotnikov@virtuozzo.com>
Cc: "Dr . David Alan Gilbert" <dgilbert@redhat.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: "Kirill A . Shutemov" <kirill@shutemov.name>
Cc: Martin Cracauer <cracauer@cons.org>
Cc: Marty McFadden <mcfadden8@llnl.gov>
Cc: Maya Gokhale <gokhale2@llnl.gov>
Cc: Mel Gorman <mgorman@suse.de>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Mike Rapoport <rppt@linux.vnet.ibm.com>
Cc: Pavel Emelyanov <xemul@openvz.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Shaohua Li <shli@fb.com>
Link: http://lkml.kernel.org/r/20200220163112.11409-14-peterx@redhat.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Andrea Arcangeli 2020-04-06 20:06:12 -07:00 committed by Linus Torvalds
parent ffd0579396
commit 63b2d4174c
2 changed files with 89 additions and 16 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

82
fs/userfaultfd.c
View file

@ -314,8 +314,11 @@ static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx,
if (!pmd_present(_pmd))
goto out;
if (pmd_trans_huge(_pmd))
if (pmd_trans_huge(_pmd)) {
if (!pmd_write(_pmd) && (reason & VM_UFFD_WP))
ret = true;
goto out;
}
/*
* the pmd is stable (as in !pmd_trans_unstable) so we can re-read it
@ -328,6 +331,8 @@ static inline bool userfaultfd_must_wait(struct userfaultfd_ctx *ctx,
*/
if (pte_none(*pte))
ret = true;
if (!pte_write(*pte) && (reason & VM_UFFD_WP))
ret = true;
pte_unmap(pte);
out:
@ -1287,10 +1292,13 @@ static __always_inline int validate_range(struct mm_struct *mm,
return 0;
}
static inline bool vma_can_userfault(struct vm_area_struct *vma)
static inline bool vma_can_userfault(struct vm_area_struct *vma,
unsigned long vm_flags)
{
return vma_is_anonymous(vma) || is_vm_hugetlb_page(vma) ||
vma_is_shmem(vma);
/* FIXME: add WP support to hugetlbfs and shmem */
return vma_is_anonymous(vma) ||
((is_vm_hugetlb_page(vma) || vma_is_shmem(vma)) &&
!(vm_flags & VM_UFFD_WP));
}
static int userfaultfd_register(struct userfaultfd_ctx *ctx,
@ -1322,15 +1330,8 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
vm_flags = 0;
if (uffdio_register.mode & UFFDIO_REGISTER_MODE_MISSING)
vm_flags |= VM_UFFD_MISSING;
if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP) {
if (uffdio_register.mode & UFFDIO_REGISTER_MODE_WP)
vm_flags |= VM_UFFD_WP;
/*
* FIXME: remove the below error constraint by
* implementing the wprotect tracking mode.
*/
ret = -EINVAL;
goto out;
}
ret = validate_range(mm, &uffdio_register.range.start,
uffdio_register.range.len);
@ -1380,7 +1381,7 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
/* check not compatible vmas */
ret = -EINVAL;
if (!vma_can_userfault(cur))
if (!vma_can_userfault(cur, vm_flags))
goto out_unlock;
/*
@ -1408,6 +1409,8 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
if (end & (vma_hpagesize - 1))
goto out_unlock;
}
if ((vm_flags & VM_UFFD_WP) && !(cur->vm_flags & VM_MAYWRITE))
goto out_unlock;
/*
* Check that this vma isn't already owned by a
@ -1437,7 +1440,7 @@ static int userfaultfd_register(struct userfaultfd_ctx *ctx,
do {
cond_resched();
BUG_ON(!vma_can_userfault(vma));
BUG_ON(!vma_can_userfault(vma, vm_flags));
BUG_ON(vma->vm_userfaultfd_ctx.ctx &&
vma->vm_userfaultfd_ctx.ctx != ctx);
WARN_ON(!(vma->vm_flags & VM_MAYWRITE));
@ -1575,7 +1578,7 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
* provides for more strict behavior to notice
* unregistration errors.
*/
if (!vma_can_userfault(cur))
if (!vma_can_userfault(cur, cur->vm_flags))
goto out_unlock;
found = true;
@ -1589,7 +1592,7 @@ static int userfaultfd_unregister(struct userfaultfd_ctx *ctx,
do {
cond_resched();
BUG_ON(!vma_can_userfault(vma));
BUG_ON(!vma_can_userfault(vma, vma->vm_flags));
/*
* Nothing to do: this vma is already registered into this
@ -1802,6 +1805,50 @@ static int userfaultfd_zeropage(struct userfaultfd_ctx *ctx,
return ret;
}
static int userfaultfd_writeprotect(struct userfaultfd_ctx *ctx,
unsigned long arg)
{
int ret;
struct uffdio_writeprotect uffdio_wp;
struct uffdio_writeprotect __user *user_uffdio_wp;
struct userfaultfd_wake_range range;
if (READ_ONCE(ctx->mmap_changing))
return -EAGAIN;
user_uffdio_wp = (struct uffdio_writeprotect __user *) arg;
if (copy_from_user(&uffdio_wp, user_uffdio_wp,
sizeof(struct uffdio_writeprotect)))
return -EFAULT;
ret = validate_range(ctx->mm, &uffdio_wp.range.start,
uffdio_wp.range.len);
if (ret)
return ret;
if (uffdio_wp.mode & ~(UFFDIO_WRITEPROTECT_MODE_DONTWAKE |
UFFDIO_WRITEPROTECT_MODE_WP))
return -EINVAL;
if ((uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_WP) &&
(uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_DONTWAKE))
return -EINVAL;
ret = mwriteprotect_range(ctx->mm, uffdio_wp.range.start,
uffdio_wp.range.len, uffdio_wp.mode &
UFFDIO_WRITEPROTECT_MODE_WP,
&ctx->mmap_changing);
if (ret)
return ret;
if (!(uffdio_wp.mode & UFFDIO_WRITEPROTECT_MODE_DONTWAKE)) {
range.start = uffdio_wp.range.start;
range.len = uffdio_wp.range.len;
wake_userfault(ctx, &range);
}
return ret;
}
static inline unsigned int uffd_ctx_features(__u64 user_features)
{
/*
@ -1883,6 +1930,9 @@ static long userfaultfd_ioctl(struct file *file, unsigned cmd,
case UFFDIO_ZEROPAGE:
ret = userfaultfd_zeropage(ctx, arg);
break;
case UFFDIO_WRITEPROTECT:
ret = userfaultfd_writeprotect(ctx, arg);
break;
}
return ret;
}

23
include/uapi/linux/userfaultfd.h
View file

@ -52,6 +52,7 @@
#define _UFFDIO_WAKE (0x02)
#define _UFFDIO_COPY (0x03)
#define _UFFDIO_ZEROPAGE (0x04)
#define _UFFDIO_WRITEPROTECT (0x06)
#define _UFFDIO_API (0x3F)
/* userfaultfd ioctl ids */
@ -68,6 +69,8 @@
struct uffdio_copy)
#define UFFDIO_ZEROPAGE _IOWR(UFFDIO, _UFFDIO_ZEROPAGE, \
struct uffdio_zeropage)
#define UFFDIO_WRITEPROTECT _IOWR(UFFDIO, _UFFDIO_WRITEPROTECT, \
struct uffdio_writeprotect)
/* read() structure */
struct uffd_msg {
@ -232,4 +235,24 @@ struct uffdio_zeropage {
__s64 zeropage;
};
struct uffdio_writeprotect {
struct uffdio_range range;
/*
* UFFDIO_WRITEPROTECT_MODE_WP: set the flag to write protect a range,
* unset the flag to undo protection of a range which was previously
* write protected.
*
* UFFDIO_WRITEPROTECT_MODE_DONTWAKE: set the flag to avoid waking up
* any wait thread after the operation succeeds.
*
* NOTE: Write protecting a region (WP=1) is unrelated to page faults,
* therefore DONTWAKE flag is meaningless with WP=1. Removing write
* protection (WP=0) in response to a page fault wakes the faulting
* task unless DONTWAKE is set.
*/
#define UFFDIO_WRITEPROTECT_MODE_WP ((__u64)1<<0)
#define UFFDIO_WRITEPROTECT_MODE_DONTWAKE ((__u64)1<<1)
__u64 mode;
};
#endif /* _LINUX_USERFAULTFD_H */