[PATCH] mm: zswap: fix kernel BUG in sg_init_one

[Barry Song <21cnbao@gmail.com>]

From: Barry Song <v-songbaohua@oppo.com>

sg_init_one() relies on linearly mapped low memory for the safe
utilization of virt_to_page(). Consequently, we have two choices:
either employ kmap_to_page() alongside sg_set_page(), or resort to
copying high memory contents to a temporary buffer residing in low
memory. However, considering the introduction of the WARN_ON_ONCE
in commit ef6e06b2ef870 ("highmem: fix kmap_to_page() for
kmap_local_page() addresses"), which specifically addresses high
memory concerns, it appears that memcpy remains the sole viable
option.

Reported-and-tested-by: syzbot+adbc983a1588b7805de3@syzkaller.appspotmail.com
Closes: https://lore.kernel.org/all/000000000000bbb3d80613f243a6@google.com/
Fixes: 270700dd06ca ("mm/zswap: remove the memcpy if acomp is not sleepable")
Signed-off-by: Barry Song <v-songbaohua@oppo.com>
---
 mm/zswap.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/zswap.c b/mm/zswap.c
index 9dec853647c8..17bf6d87b274 100644
--- a/mm/zswap.c
+++ b/mm/zswap.c
@@ -1080,7 +1080,8 @@ static void zswap_decompress(struct zswap_entry *entry, struct page *page)
 	mutex_lock(&acomp_ctx->mutex);
 
 	src = zpool_map_handle(zpool, entry->handle, ZPOOL_MM_RO);
-	if (acomp_ctx->is_sleepable && !zpool_can_sleep_mapped(zpool)) {
+	if ((acomp_ctx->is_sleepable && !zpool_can_sleep_mapped(zpool)) ||
+	    !virt_addr_valid(src)) {
 		memcpy(acomp_ctx->buffer, src, entry->length);
 		src = acomp_ctx->buffer;
 		zpool_unmap_handle(zpool, entry->handle);
@@ -1094,7 +1095,7 @@ static void zswap_decompress(struct zswap_entry *entry, struct page *page)
 	BUG_ON(acomp_ctx->req->dlen != PAGE_SIZE);
 	mutex_unlock(&acomp_ctx->mutex);
 
-	if (!acomp_ctx->is_sleepable || zpool_can_sleep_mapped(zpool))
+	if (src != acomp_ctx->buffer)
 		zpool_unmap_handle(zpool, entry->handle);
 }
 
-- 
2.34.1