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Subject[PATCH 5/6] dax,pmem: Add data recovery feature to pmem_copy_to/from_iter()
Date
When DAXDEV_F_RECOVERY flag is set, pmem_copy_to_iter() shall read
as much data as possible up till the first poisoned page is
encountered, and pmem_copy_from_iter() shall try to clear poison(s)
within the page aligned range prior to writing.

Signed-off-by: Jane Chu <jane.chu@oracle.com>
---
drivers/nvdimm/pmem.c | 72 ++++++++++++++++++++++++++++++++++++++++---
fs/dax.c | 5 +++
2 files changed, 72 insertions(+), 5 deletions(-)

diff --git a/drivers/nvdimm/pmem.c b/drivers/nvdimm/pmem.c
index e2a1c35108cd..c456f84d2f6f 100644
--- a/drivers/nvdimm/pmem.c
+++ b/drivers/nvdimm/pmem.c
@@ -305,21 +305,83 @@ static long pmem_dax_direct_access(struct dax_device *dax_dev,
}

/*
- * Use the 'no check' versions of copy_from_iter_flushcache() and
- * copy_mc_to_iter() to bypass HARDENED_USERCOPY overhead. Bounds
- * checking, both file offset and device offset, is handled by
- * dax_iomap_actor()
+ * Even though the 'no check' versions of copy_from_iter_flushcache()
+ * and copy_mc_to_iter() are used to bypass HARDENED_USERCOPY overhead,
+ * 'read'/'write' aren't always safe when poison is consumed. They happen
+ * to be safe because the 'read'/'write' range has been guaranteed
+ * be free of poison(s) by a prior call to dax_direct_access() on the
+ * caller stack.
+ * However with the introduction of DAXDEV_F_RECOVERY, the 'read'/'write'
+ * range may contain poison(s), so the functions perform explicit check
+ * on poison, and 'read' end up fetching only non-poisoned page(s) up
+ * till the first poison is encountered while 'write' require the range
+ * is page aligned in order to restore the poisoned page's memory type
+ * back to "rw" after clearing the poison(s).
+ * In the event of poison related failure, (size_t) -EIO is returned and
+ * caller may check the return value after casting it to (ssize_t).
*/
static size_t pmem_copy_from_iter(struct dax_device *dax_dev, pgoff_t pgoff,
void *addr, size_t bytes, struct iov_iter *i, unsigned long flags)
{
+ phys_addr_t pmem_off;
+ size_t len, lead_off;
+ struct pmem_device *pmem = dax_get_private(dax_dev);
+ struct device *dev = pmem->bb.dev;
+
+ if (flags & DAXDEV_F_RECOVERY) {
+ lead_off = (unsigned long)addr & ~PAGE_MASK;
+ len = PFN_PHYS(PFN_UP(lead_off + bytes));
+ if (is_bad_pmem(&pmem->bb, PFN_PHYS(pgoff) / 512, len)) {
+ if (lead_off || !(PAGE_ALIGNED(bytes))) {
+ dev_warn(dev, "Found poison, but addr(%p) and/or bytes(%#lx) not page aligned\n",
+ addr, bytes);
+ return (size_t) -EIO;
+ }
+ pmem_off = PFN_PHYS(pgoff) + pmem->data_offset;
+ if (pmem_clear_poison(pmem, pmem_off, bytes) !=
+ BLK_STS_OK)
+ return (size_t) -EIO;
+ }
+ }
+
return _copy_from_iter_flushcache(addr, bytes, i);
}

static size_t pmem_copy_to_iter(struct dax_device *dax_dev, pgoff_t pgoff,
void *addr, size_t bytes, struct iov_iter *i, unsigned long flags)
{
- return _copy_mc_to_iter(addr, bytes, i);
+ int num_bad;
+ size_t len, lead_off;
+ unsigned long bad_pfn;
+ bool bad_pmem = false;
+ size_t adj_len = bytes;
+ sector_t sector, first_bad;
+ struct pmem_device *pmem = dax_get_private(dax_dev);
+ struct device *dev = pmem->bb.dev;
+
+ if (flags & DAXDEV_F_RECOVERY) {
+ sector = PFN_PHYS(pgoff) / 512;
+ lead_off = (unsigned long)addr & ~PAGE_MASK;
+ len = PFN_PHYS(PFN_UP(lead_off + bytes));
+ if (pmem->bb.count)
+ bad_pmem = !!badblocks_check(&pmem->bb, sector,
+ len / 512, &first_bad, &num_bad);
+ if (bad_pmem) {
+ bad_pfn = PHYS_PFN(first_bad * 512);
+ if (bad_pfn == pgoff) {
+ dev_warn(dev, "Found poison in page: pgoff(%#lx)\n",
+ pgoff);
+ return -EIO;
+ }
+ adj_len = PFN_PHYS(bad_pfn - pgoff) - lead_off;
+ dev_WARN_ONCE(dev, (adj_len > bytes),
+ "out-of-range first_bad?");
+ }
+ if (adj_len == 0)
+ return (size_t) -EIO;
+ }
+
+ return _copy_mc_to_iter(addr, adj_len, i);
}

static const struct dax_operations pmem_dax_ops = {
diff --git a/fs/dax.c b/fs/dax.c
index 69433c6cd6c4..b9286668dc46 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -1246,6 +1246,11 @@ static loff_t dax_iomap_iter(const struct iomap_iter *iomi,
xfer = dax_copy_to_iter(dax_dev, pgoff, kaddr,
map_len, iter, dax_flag);

+ if ((ssize_t)xfer == -EIO) {
+ ret = -EIO;
+ break;
+ }
+
pos += xfer;
length -= xfer;
done += xfer;
--
2.18.4
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