From f9e040efcc28309e5c592f7e79085a9a52e31f58 Mon Sep 17 00:00:00 2001
From: Mikulas Patocka <mpatocka@redhat.com>
Date: Mon, 24 Aug 2020 11:09:47 -0400
Subject: [PATCH] dm writecache: handle DAX to partitions on persistent memory
 correctly
Git-commit: f9e040efcc28309e5c592f7e79085a9a52e31f58
Patch-mainline: v5.9-rc4
References: git-fixes

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 <mpatocka@redhat.com>
Fixes: 48debafe4f2f ("dm: add writecache target")
Cc: stable@vger.kernel.org # 4.18+
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Coly Li <colyli@suse.de>

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

diff --git a/drivers/md/dm-writecache.c b/drivers/md/dm-writecache.c
index 86dbe0c8b45c..6271d1e741cf 100644
--- a/drivers/md/dm-writecache.c
+++ b/drivers/md/dm-writecache.c
@@ -231,6 +231,7 @@ static int persistent_memory_claim(struct dm_writecache *wc)
 	pfn_t pfn;
 	int id;
 	struct page **pages;
+	sector_t offset;
 
 	wc->memory_vmapped = false;
 
@@ -245,9 +246,16 @@ static int persistent_memory_claim(struct dm_writecache *wc)
 		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(struct dm_writecache *wc)
 		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;
-- 
2.31.1