linux-kernel - [PATCH v6 2/6] dax: fix cache flush on PMD-mapped pages

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Message-Id: <20220329134853.68403-3-songmuchun@bytedance.com>
Date:   Tue, 29 Mar 2022 21:48:49 +0800
From:   Muchun Song <songmuchun@...edance.com>
To:     dan.j.williams@...el.com, willy@...radead.org, jack@...e.cz,
        viro@...iv.linux.org.uk, akpm@...ux-foundation.org,
        apopple@...dia.com, shy828301@...il.com, rcampbell@...dia.com,
        hughd@...gle.com, xiyuyang19@...an.edu.cn,
        kirill.shutemov@...ux.intel.com, zwisler@...nel.org,
        hch@...radead.org
Cc:     linux-fsdevel@...r.kernel.org, nvdimm@...ts.linux.dev,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        duanxiongchun@...edance.com, smuchun@...il.com,
        Muchun Song <songmuchun@...edance.com>,
        Christoph Hellwig <hch@....de>
Subject: [PATCH v6 2/6] dax: fix cache flush on PMD-mapped pages

The flush_cache_page() only remove a PAGE_SIZE sized range from the cache.
However, it does not cover the full pages in a THP except a head page.
Replace it with flush_cache_range() to fix this issue.  This is just a
documentation issue with the respect to properly documenting the expected
usage of cache flushing before modifying the pmd.  However, in practice
this is not a problem due to the fact that DAX is not available on
architectures with virtually indexed caches per:

  commit d92576f1167c ("dax: does not work correctly with virtual aliasing caches")

Fixes: f729c8c9b24f ("dax: wrprotect pmd_t in dax_mapping_entry_mkclean")
Signed-off-by: Muchun Song <songmuchun@...edance.com>
Reviewed-by: Dan Williams <dan.j.williams@...el.com>
Reviewed-by: Christoph Hellwig <hch@....de>
---
 fs/dax.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/dax.c b/fs/dax.c
index 67a08a32fccb..a372304c9695 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -845,7 +845,8 @@ static void dax_entry_mkclean(struct address_space *mapping, pgoff_t index,
 			if (!pmd_dirty(*pmdp) && !pmd_write(*pmdp))
 				goto unlock_pmd;
 
-			flush_cache_page(vma, address, pfn);
+			flush_cache_range(vma, address,
+					  address + HPAGE_PMD_SIZE);
 			pmd = pmdp_invalidate(vma, address, pmdp);
 			pmd = pmd_wrprotect(pmd);
 			pmd = pmd_mkclean(pmd);
-- 
2.11.0