The patch titled
Subject: fsdax: zero the edges if source is HOLE or UNWRITTEN
has been added to the -mm mm-unstable branch. Its filename is
fsdax-zero-the-edges-if-source-is-hole-or-unwritten.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/fsdax-zero-the-edges-if-source-is-hole-or-unwritten.patch
This patch will later appear in the mm-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Shiyang Ruan <ruansy.fnst@xxxxxxxxxxx>
Subject: fsdax: zero the edges if source is HOLE or UNWRITTEN
Date: Thu, 1 Dec 2022 15:28:53 +0000
If srcmap contains invalid data, such as HOLE and UNWRITTEN, the dest page
should be zeroed. Otherwise, since it's a pmem, old data may remains on
the dest page, the result of CoW will be incorrect.
The function name is also not easy to understand, rename it to
"dax_iomap_copy_around()", which means it copys data around the range.
Link: https://lkml.kernel.org/r/1669908538-55-4-git-send-email-ruansy.fnst@xxxxxxxxxxx
Signed-off-by: Shiyang Ruan <ruansy.fnst@xxxxxxxxxxx>
Cc: Alistair Popple <apopple@xxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: Dave Chinner <david@xxxxxxxxxxxxx>
Cc: Jason Gunthorpe <jgg@xxxxxxxxxx>
Cc: John Hubbard <jhubbard@xxxxxxxxxx>
Cc: Darrick J. Wong <djwong@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
fs/dax.c | 78 ++++++++++++++++++++++++++++++++---------------------
1 file changed, 48 insertions(+), 30 deletions(-)
--- a/fs/dax.c~fsdax-zero-the-edges-if-source-is-hole-or-unwritten
+++ a/fs/dax.c
@@ -1092,7 +1092,7 @@ out:
}
/**
- * dax_iomap_cow_copy - Copy the data from source to destination before write
+ * dax_iomap_copy_around - Copy the data from source to destination before write
* @pos: address to do copy from.
* @length: size of copy operation.
* @align_size: aligned w.r.t align_size (either PMD_SIZE or PAGE_SIZE)
@@ -1101,35 +1101,50 @@ out:
*
* This can be called from two places. Either during DAX write fault (page
* aligned), to copy the length size data to daddr. Or, while doing normal DAX
- * write operation, dax_iomap_actor() might call this to do the copy of either
+ * write operation, dax_iomap_iter() might call this to do the copy of either
* start or end unaligned address. In the latter case the rest of the copy of
- * aligned ranges is taken care by dax_iomap_actor() itself.
+ * aligned ranges is taken care by dax_iomap_iter() itself.
+ * If the srcmap contains invalid data, such as HOLE and UNWRITTEN, zero the
+ * area to make sure no old data remains.
*/
-static int dax_iomap_cow_copy(loff_t pos, uint64_t length, size_t align_size,
+static int dax_iomap_copy_around(loff_t pos, uint64_t length, size_t align_size,
const struct iomap *srcmap, void *daddr)
{
loff_t head_off = pos & (align_size - 1);
size_t size = ALIGN(head_off + length, align_size);
loff_t end = pos + length;
loff_t pg_end = round_up(end, align_size);
+ /* copy_all is usually in page fault case */
bool copy_all = head_off == 0 && end == pg_end;
+ /* zero the edges if srcmap is a HOLE or IOMAP_UNWRITTEN */
+ bool zero_edge = srcmap->flags & IOMAP_F_SHARED ||
+ srcmap->type == IOMAP_UNWRITTEN;
void *saddr = 0;
int ret = 0;
- ret = dax_iomap_direct_access(srcmap, pos, size, &saddr, NULL);
- if (ret)
- return ret;
+ if (!zero_edge) {
+ ret = dax_iomap_direct_access(srcmap, pos, size, &saddr, NULL);
+ if (ret)
+ return ret;
+ }
if (copy_all) {
- ret = copy_mc_to_kernel(daddr, saddr, length);
- return ret ? -EIO : 0;
+ if (zero_edge)
+ memset(daddr, 0, size);
+ else
+ ret = copy_mc_to_kernel(daddr, saddr, length);
+ goto out;
}
/* Copy the head part of the range */
if (head_off) {
- ret = copy_mc_to_kernel(daddr, saddr, head_off);
- if (ret)
- return -EIO;
+ if (zero_edge)
+ memset(daddr, 0, head_off);
+ else {
+ ret = copy_mc_to_kernel(daddr, saddr, head_off);
+ if (ret)
+ return -EIO;
+ }
}
/* Copy the tail part of the range */
@@ -1137,12 +1152,19 @@ static int dax_iomap_cow_copy(loff_t pos
loff_t tail_off = head_off + length;
loff_t tail_len = pg_end - end;
- ret = copy_mc_to_kernel(daddr + tail_off, saddr + tail_off,
- tail_len);
- if (ret)
- return -EIO;
+ if (zero_edge)
+ memset(daddr + tail_off, 0, tail_len);
+ else {
+ ret = copy_mc_to_kernel(daddr + tail_off,
+ saddr + tail_off, tail_len);
+ if (ret)
+ return -EIO;
+ }
}
- return 0;
+out:
+ if (zero_edge)
+ dax_flush(srcmap->dax_dev, daddr, size);
+ return ret ? -EIO : 0;
}
/*
@@ -1241,13 +1263,10 @@ static int dax_memzero(struct iomap_iter
if (ret < 0)
return ret;
memset(kaddr + offset, 0, size);
- if (srcmap->addr != iomap->addr) {
- ret = dax_iomap_cow_copy(pos, size, PAGE_SIZE, srcmap,
- kaddr);
- if (ret < 0)
- return ret;
- dax_flush(iomap->dax_dev, kaddr, PAGE_SIZE);
- } else
+ if (iomap->flags & IOMAP_F_SHARED)
+ ret = dax_iomap_copy_around(pos, size, PAGE_SIZE, srcmap,
+ kaddr);
+ else
dax_flush(iomap->dax_dev, kaddr + offset, size);
return ret;
}
@@ -1401,8 +1420,8 @@ static loff_t dax_iomap_iter(const struc
}
if (cow) {
- ret = dax_iomap_cow_copy(pos, length, PAGE_SIZE, srcmap,
- kaddr);
+ ret = dax_iomap_copy_around(pos, length, PAGE_SIZE,
+ srcmap, kaddr);
if (ret)
break;
}
@@ -1547,7 +1566,7 @@ static vm_fault_t dax_fault_iter(struct
struct xa_state *xas, void **entry, bool pmd)
{
const struct iomap *iomap = &iter->iomap;
- const struct iomap *srcmap = &iter->srcmap;
+ const struct iomap *srcmap = iomap_iter_srcmap(iter);
size_t size = pmd ? PMD_SIZE : PAGE_SIZE;
loff_t pos = (loff_t)xas->xa_index << PAGE_SHIFT;
bool write = iter->flags & IOMAP_WRITE;
@@ -1578,9 +1597,8 @@ static vm_fault_t dax_fault_iter(struct
*entry = dax_insert_entry(xas, vmf, iter, *entry, pfn, entry_flags);
- if (write &&
- srcmap->type != IOMAP_HOLE && srcmap->addr != iomap->addr) {
- err = dax_iomap_cow_copy(pos, size, size, srcmap, kaddr);
+ if (write && iomap->flags & IOMAP_F_SHARED) {
+ err = dax_iomap_copy_around(pos, size, size, srcmap, kaddr);
if (err)
return dax_fault_return(err);
}
_
Patches currently in -mm which might be from ruansy.fnst@xxxxxxxxxxx are
fsdax-introduce-page-share-for-fsdax-in-reflink-mode.patch
fsdax-invalidate-pages-when-cow.patch
fsdax-zero-the-edges-if-source-is-hole-or-unwritten.patch
fsdaxxfs-set-the-shared-flag-when-file-extent-is-shared.patch
fsdax-dedupe-iter-two-files-at-the-same-time.patch
xfs-use-dax-ops-for-zero-and-truncate-in-fsdax-mode.patch
fsdaxxfs-port-unshare-to-fsdax.patch
xfs-remove-restrictions-for-fsdax-and-reflink.patch
