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Message-Id: <20210225021420.2290912-2-axelrasmussen@google.com>
Date: Wed, 24 Feb 2021 18:14:16 -0800
From: Axel Rasmussen <axelrasmussen@...gle.com>
To: Alexander Viro <viro@...iv.linux.org.uk>,
Andrea Arcangeli <aarcange@...hat.com>,
Andrew Morton <akpm@...ux-foundation.org>,
Hugh Dickins <hughd@...gle.com>,
Jerome Glisse <jglisse@...hat.com>,
Joe Perches <joe@...ches.com>,
Lokesh Gidra <lokeshgidra@...gle.com>,
Mike Rapoport <rppt@...ux.vnet.ibm.com>,
Peter Xu <peterx@...hat.com>, Shaohua Li <shli@...com>,
Shuah Khan <shuah@...nel.org>, Wang Qing <wangqing@...o.com>
Cc: linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
linux-mm@...ck.org, linux-kselftest@...r.kernel.org,
Axel Rasmussen <axelrasmussen@...gle.com>,
Cannon Matthews <cannonmatthews@...gle.com>,
"Dr . David Alan Gilbert" <dgilbert@...hat.com>,
David Rientjes <rientjes@...gle.com>,
Michel Lespinasse <walken@...gle.com>,
Mina Almasry <almasrymina@...gle.com>,
Oliver Upton <oupton@...gle.com>
Subject: [PATCH 1/5] userfaultfd: support minor fault handling for shmem
Modify the userfaultfd register API to allow registering shmem VMAs in
minor mode. Modify the shmem mcopy implementation to support
UFFDIO_CONTINUE in order to resolve such faults.
Combine the shmem mcopy handler functions into a single
shmem_mcopy_atomic_pte, which takes a mode parameter. This matches how
the hugetlbfs implementation is structured, and lets us remove a good
chunk of boilerplate.
Signed-off-by: Axel Rasmussen <axelrasmussen@...gle.com>
---
fs/userfaultfd.c | 6 +--
include/linux/shmem_fs.h | 26 ++++------
include/uapi/linux/userfaultfd.h | 4 +-
mm/memory.c | 8 +--
mm/shmem.c | 88 +++++++++++++++-----------------
mm/userfaultfd.c | 27 +++++-----
6 files changed, 77 insertions(+), 82 deletions(-)
diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c
index 0311e9b8a8fc..aa6d584ae8c7 100644
--- a/fs/userfaultfd.c
+++ b/fs/userfaultfd.c
@@ -1267,8 +1267,7 @@ static inline bool vma_can_userfault(struct vm_area_struct *vma,
}
if (vm_flags & VM_UFFD_MINOR) {
- /* FIXME: Add minor fault interception for shmem. */
- if (!is_vm_hugetlb_page(vma))
+ if (!(is_vm_hugetlb_page(vma) || vma_is_shmem(vma)))
return false;
}
@@ -1941,7 +1940,8 @@ static int userfaultfd_api(struct userfaultfd_ctx *ctx,
/* report all available features and ioctls to userland */
uffdio_api.features = UFFD_API_FEATURES;
#ifndef CONFIG_HAVE_ARCH_USERFAULTFD_MINOR
- uffdio_api.features &= ~UFFD_FEATURE_MINOR_HUGETLBFS;
+ uffdio_api.features &=
+ ~(UFFD_FEATURE_MINOR_HUGETLBFS | UFFD_FEATURE_MINOR_SHMEM);
#endif
uffdio_api.ioctls = UFFD_API_IOCTLS;
ret = -EFAULT;
diff --git a/include/linux/shmem_fs.h b/include/linux/shmem_fs.h
index d82b6f396588..f0919c3722e7 100644
--- a/include/linux/shmem_fs.h
+++ b/include/linux/shmem_fs.h
@@ -9,6 +9,7 @@
#include <linux/percpu_counter.h>
#include <linux/xattr.h>
#include <linux/fs_parser.h>
+#include <linux/userfaultfd_k.h>
/* inode in-kernel data */
@@ -122,21 +123,16 @@ static inline bool shmem_file(struct file *file)
extern bool shmem_charge(struct inode *inode, long pages);
extern void shmem_uncharge(struct inode *inode, long pages);
+#ifdef CONFIG_USERFAULTFD
#ifdef CONFIG_SHMEM
-extern int shmem_mcopy_atomic_pte(struct mm_struct *dst_mm, pmd_t *dst_pmd,
- struct vm_area_struct *dst_vma,
- unsigned long dst_addr,
- unsigned long src_addr,
- struct page **pagep);
-extern int shmem_mfill_zeropage_pte(struct mm_struct *dst_mm,
- pmd_t *dst_pmd,
- struct vm_area_struct *dst_vma,
- unsigned long dst_addr);
-#else
-#define shmem_mcopy_atomic_pte(dst_mm, dst_pte, dst_vma, dst_addr, \
- src_addr, pagep) ({ BUG(); 0; })
-#define shmem_mfill_zeropage_pte(dst_mm, dst_pmd, dst_vma, \
- dst_addr) ({ BUG(); 0; })
-#endif
+int shmem_mcopy_atomic_pte(struct mm_struct *dst_mm, pmd_t *dst_pmd,
+ struct vm_area_struct *dst_vma,
+ unsigned long dst_addr, unsigned long src_addr,
+ enum mcopy_atomic_mode mode, struct page **pagep);
+#else /* !CONFIG_SHMEM */
+#define shmem_mcopy_atomic_pte(dst_mm, dst_pmd, dst_vma, dst_addr, \
+ src_addr, mode, pagep) ({ BUG(); 0; })
+#endif /* CONFIG_SHMEM */
+#endif /* CONFIG_USERFAULTFD */
#endif
diff --git a/include/uapi/linux/userfaultfd.h b/include/uapi/linux/userfaultfd.h
index bafbeb1a2624..47d9790d863d 100644
--- a/include/uapi/linux/userfaultfd.h
+++ b/include/uapi/linux/userfaultfd.h
@@ -31,7 +31,8 @@
UFFD_FEATURE_MISSING_SHMEM | \
UFFD_FEATURE_SIGBUS | \
UFFD_FEATURE_THREAD_ID | \
- UFFD_FEATURE_MINOR_HUGETLBFS)
+ UFFD_FEATURE_MINOR_HUGETLBFS | \
+ UFFD_FEATURE_MINOR_SHMEM)
#define UFFD_API_IOCTLS \
((__u64)1 << _UFFDIO_REGISTER | \
(__u64)1 << _UFFDIO_UNREGISTER | \
@@ -196,6 +197,7 @@ struct uffdio_api {
#define UFFD_FEATURE_SIGBUS (1<<7)
#define UFFD_FEATURE_THREAD_ID (1<<8)
#define UFFD_FEATURE_MINOR_HUGETLBFS (1<<9)
+#define UFFD_FEATURE_MINOR_SHMEM (1<<10)
__u64 features;
__u64 ioctls;
diff --git a/mm/memory.c b/mm/memory.c
index c8e357627318..a1e5ff55027e 100644
--- a/mm/memory.c
+++ b/mm/memory.c
@@ -3929,9 +3929,11 @@ static vm_fault_t do_read_fault(struct vm_fault *vmf)
* something).
*/
if (vma->vm_ops->map_pages && fault_around_bytes >> PAGE_SHIFT > 1) {
- ret = do_fault_around(vmf);
- if (ret)
- return ret;
+ if (likely(!userfaultfd_minor(vmf->vma))) {
+ ret = do_fault_around(vmf);
+ if (ret)
+ return ret;
+ }
}
ret = __do_fault(vmf);
diff --git a/mm/shmem.c b/mm/shmem.c
index 06c771d23127..d7847f6f696b 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -77,7 +77,6 @@ static struct vfsmount *shm_mnt;
#include <linux/syscalls.h>
#include <linux/fcntl.h>
#include <uapi/linux/memfd.h>
-#include <linux/userfaultfd_k.h>
#include <linux/rmap.h>
#include <linux/uuid.h>
@@ -1781,8 +1780,8 @@ static int shmem_swapin_page(struct inode *inode, pgoff_t index,
* vm. If we swap it in we mark it dirty since we also free the swap
* entry since a page cannot live in both the swap and page cache.
*
- * vmf and fault_type are only supplied by shmem_fault:
- * otherwise they are NULL.
+ * vma, vmf, and fault_type are only supplied by shmem_fault: otherwise they
+ * are NULL.
*/
static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
struct page **pagep, enum sgp_type sgp, gfp_t gfp,
@@ -1826,6 +1825,12 @@ static int shmem_getpage_gfp(struct inode *inode, pgoff_t index,
return error;
}
+ if (page && vma && userfaultfd_minor(vma)) {
+ unlock_page(page);
+ *fault_type = handle_userfault(vmf, VM_UFFD_MINOR);
+ return 0;
+ }
+
if (page)
hindex = page->index;
if (page && sgp == SGP_WRITE)
@@ -2350,14 +2355,12 @@ static struct inode *shmem_get_inode(struct super_block *sb, const struct inode
return inode;
}
-static int shmem_mfill_atomic_pte(struct mm_struct *dst_mm,
- pmd_t *dst_pmd,
- struct vm_area_struct *dst_vma,
- unsigned long dst_addr,
- unsigned long src_addr,
- bool zeropage,
- struct page **pagep)
+int shmem_mcopy_atomic_pte(struct mm_struct *dst_mm, pmd_t *dst_pmd,
+ struct vm_area_struct *dst_vma,
+ unsigned long dst_addr, unsigned long src_addr,
+ enum mcopy_atomic_mode mode, struct page **pagep)
{
+ bool is_continue = (mode == MCOPY_ATOMIC_CONTINUE);
struct inode *inode = file_inode(dst_vma->vm_file);
struct shmem_inode_info *info = SHMEM_I(inode);
struct address_space *mapping = inode->i_mapping;
@@ -2374,12 +2377,17 @@ static int shmem_mfill_atomic_pte(struct mm_struct *dst_mm,
if (!shmem_inode_acct_block(inode, 1))
goto out;
- if (!*pagep) {
+ if (is_continue) {
+ ret = -EFAULT;
+ page = find_get_page(mapping, pgoff);
+ if (!page)
+ goto out_unacct_blocks;
+ } else if (!*pagep) {
page = shmem_alloc_page(gfp, info, pgoff);
if (!page)
goto out_unacct_blocks;
- if (!zeropage) { /* mcopy_atomic */
+ if (mode == MCOPY_ATOMIC_NORMAL) { /* mcopy_atomic */
page_kaddr = kmap_atomic(page);
ret = copy_from_user(page_kaddr,
(const void __user *)src_addr,
@@ -2393,7 +2401,7 @@ static int shmem_mfill_atomic_pte(struct mm_struct *dst_mm,
/* don't free the page */
return -ENOENT;
}
- } else { /* mfill_zeropage_atomic */
+ } else { /* zeropage */
clear_highpage(page);
}
} else {
@@ -2401,9 +2409,12 @@ static int shmem_mfill_atomic_pte(struct mm_struct *dst_mm,
*pagep = NULL;
}
- VM_BUG_ON(PageLocked(page) || PageSwapBacked(page));
+ if (!is_continue)
+ VM_BUG_ON(PageSwapBacked(page));
+ VM_BUG_ON(PageLocked(page));
__SetPageLocked(page);
- __SetPageSwapBacked(page);
+ if (!is_continue || !PageSwapBacked(page))
+ __SetPageSwapBacked(page);
__SetPageUptodate(page);
ret = -EFAULT;
@@ -2412,10 +2423,13 @@ static int shmem_mfill_atomic_pte(struct mm_struct *dst_mm,
if (unlikely(offset >= max_off))
goto out_release;
- ret = shmem_add_to_page_cache(page, mapping, pgoff, NULL,
- gfp & GFP_RECLAIM_MASK, dst_mm);
- if (ret)
- goto out_release;
+ /* If page wasn't already in the page cache, add it. */
+ if (!is_continue) {
+ ret = shmem_add_to_page_cache(page, mapping, pgoff, NULL,
+ gfp & GFP_RECLAIM_MASK, dst_mm);
+ if (ret)
+ goto out_release;
+ }
_dst_pte = mk_pte(page, dst_vma->vm_page_prot);
if (dst_vma->vm_flags & VM_WRITE)
@@ -2442,13 +2456,15 @@ static int shmem_mfill_atomic_pte(struct mm_struct *dst_mm,
if (!pte_none(*dst_pte))
goto out_release_unlock;
- lru_cache_add(page);
+ if (!is_continue) {
+ lru_cache_add(page);
- spin_lock_irq(&info->lock);
- info->alloced++;
- inode->i_blocks += BLOCKS_PER_PAGE;
- shmem_recalc_inode(inode);
- spin_unlock_irq(&info->lock);
+ spin_lock_irq(&info->lock);
+ info->alloced++;
+ inode->i_blocks += BLOCKS_PER_PAGE;
+ shmem_recalc_inode(inode);
+ spin_unlock_irq(&info->lock);
+ }
inc_mm_counter(dst_mm, mm_counter_file(page));
page_add_file_rmap(page, false);
@@ -2473,28 +2489,6 @@ static int shmem_mfill_atomic_pte(struct mm_struct *dst_mm,
goto out;
}
-int shmem_mcopy_atomic_pte(struct mm_struct *dst_mm,
- pmd_t *dst_pmd,
- struct vm_area_struct *dst_vma,
- unsigned long dst_addr,
- unsigned long src_addr,
- struct page **pagep)
-{
- return shmem_mfill_atomic_pte(dst_mm, dst_pmd, dst_vma,
- dst_addr, src_addr, false, pagep);
-}
-
-int shmem_mfill_zeropage_pte(struct mm_struct *dst_mm,
- pmd_t *dst_pmd,
- struct vm_area_struct *dst_vma,
- unsigned long dst_addr)
-{
- struct page *page = NULL;
-
- return shmem_mfill_atomic_pte(dst_mm, dst_pmd, dst_vma,
- dst_addr, 0, true, &page);
-}
-
#ifdef CONFIG_TMPFS
static const struct inode_operations shmem_symlink_inode_operations;
static const struct inode_operations shmem_short_symlink_operations;
diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
index ce6cb4760d2c..6cd7ab531aec 100644
--- a/mm/userfaultfd.c
+++ b/mm/userfaultfd.c
@@ -415,7 +415,7 @@ static __always_inline ssize_t mfill_atomic_pte(struct mm_struct *dst_mm,
unsigned long dst_addr,
unsigned long src_addr,
struct page **page,
- bool zeropage,
+ enum mcopy_atomic_mode mode,
bool wp_copy)
{
ssize_t err;
@@ -431,22 +431,24 @@ static __always_inline ssize_t mfill_atomic_pte(struct mm_struct *dst_mm,
* and not in the radix tree.
*/
if (!(dst_vma->vm_flags & VM_SHARED)) {
- if (!zeropage)
+ switch (mode) {
+ case MCOPY_ATOMIC_NORMAL:
err = mcopy_atomic_pte(dst_mm, dst_pmd, dst_vma,
dst_addr, src_addr, page,
wp_copy);
- else
+ break;
+ case MCOPY_ATOMIC_ZEROPAGE:
err = mfill_zeropage_pte(dst_mm, dst_pmd,
dst_vma, dst_addr);
+ break;
+ case MCOPY_ATOMIC_CONTINUE:
+ err = -EINVAL;
+ break;
+ }
} else {
VM_WARN_ON_ONCE(wp_copy);
- if (!zeropage)
- err = shmem_mcopy_atomic_pte(dst_mm, dst_pmd,
- dst_vma, dst_addr,
- src_addr, page);
- else
- err = shmem_mfill_zeropage_pte(dst_mm, dst_pmd,
- dst_vma, dst_addr);
+ err = shmem_mcopy_atomic_pte(dst_mm, dst_pmd, dst_vma, dst_addr,
+ src_addr, mode, page);
}
return err;
@@ -467,7 +469,6 @@ static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,
long copied;
struct page *page;
bool wp_copy;
- bool zeropage = (mcopy_mode == MCOPY_ATOMIC_ZEROPAGE);
/*
* Sanitize the command parameters:
@@ -530,7 +531,7 @@ static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,
if (!vma_is_anonymous(dst_vma) && !vma_is_shmem(dst_vma))
goto out_unlock;
- if (mcopy_mode == MCOPY_ATOMIC_CONTINUE)
+ if (!vma_is_shmem(dst_vma) && mcopy_mode == MCOPY_ATOMIC_CONTINUE)
goto out_unlock;
/*
@@ -578,7 +579,7 @@ static __always_inline ssize_t __mcopy_atomic(struct mm_struct *dst_mm,
BUG_ON(pmd_trans_huge(*dst_pmd));
err = mfill_atomic_pte(dst_mm, dst_pmd, dst_vma, dst_addr,
- src_addr, &page, zeropage, wp_copy);
+ src_addr, &page, mcopy_mode, wp_copy);
cond_resched();
if (unlikely(err == -ENOENT)) {
--
2.30.0.617.g56c4b15f3c-goog
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