[PATCH 5.8 165/186] dm writecache: handle DAX to partitions on persistent memory correctly

[Greg Kroah-Hartman]

From: Mikulas Patocka <mpato...@redhat.com>

commit f9e040efcc28309e5c592f7e79085a9a52e31f58 upstream.

The function dax_direct_access doesn't take partitions into account,
it always maps pages from the beginning of the device. Therefore,
persistent_memory_claim() must get the partition offset using
get_start_sect() and add it to the page offsets passed to
dax_direct_access().

Signed-off-by: Mikulas Patocka <mpato...@redhat.com>
Fixes: 48debafe4f2f ("dm: add writecache target")
Cc: sta...@vger.kernel.org # 4.18+
Signed-off-by: Mike Snitzer <snit...@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gre...@linuxfoundation.org>

---
 drivers/md/dm-writecache.c |   12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

--- a/drivers/md/dm-writecache.c
+++ b/drivers/md/dm-writecache.c
@@ -231,6 +231,7 @@ static int persistent_memory_claim(struc
        pfn_t pfn;
        int id;
        struct page **pages;
+       sector_t offset;
 
        wc->memory_vmapped = false;
 
@@ -245,9 +246,16 @@ static int persistent_memory_claim(struc
                goto err1;
        }
 
+       offset = get_start_sect(wc->ssd_dev->bdev);
+       if (offset & (PAGE_SIZE / 512 - 1)) {
+               r = -EINVAL;
+               goto err1;
+       }
+       offset >>= PAGE_SHIFT - 9;
+
        id = dax_read_lock();
 
-       da = dax_direct_access(wc->ssd_dev->dax_dev, 0, p, &wc->memory_map, 
&pfn);
+       da = dax_direct_access(wc->ssd_dev->dax_dev, offset, p, 
&wc->memory_map, &pfn);
        if (da < 0) {
                wc->memory_map = NULL;
                r = da;
@@ -269,7 +277,7 @@ static int persistent_memory_claim(struc
                i = 0;
                do {
                        long daa;
-                       daa = dax_direct_access(wc->ssd_dev->dax_dev, i, p - i,
+                       daa = dax_direct_access(wc->ssd_dev->dax_dev, offset + 
i, p - i,
                                                NULL, &pfn);
                        if (daa <= 0) {
                                r = daa ? daa : -EINVAL;