linux-kernel - [PATCH 01/18] mm: add a kunmap_local

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Date:   Tue, 15 Jun 2021 15:24:39 +0200
From:   Christoph Hellwig <hch@....de>
To:     Jens Axboe <axboe@...nel.dk>, Thomas Gleixner <tglx@...utronix.de>
Cc:     Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Geoff Levand <geoff@...radead.org>,
        Ilya Dryomov <idryomov@...il.com>,
        Dongsheng Yang <dongsheng.yang@...ystack.cn>,
        Mike Snitzer <snitzer@...hat.com>,
        "James E.J. Bottomley" <James.Bottomley@...senPartnership.com>,
        Ira Weiny <ira.weiny@...el.com>, dm-devel@...hat.com,
        linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-block@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        ceph-devel@...r.kernel.org, linux-arch@...r.kernel.org
Subject: [PATCH 01/18] mm: add a kunmap_local_dirty helper

Add a helper that calls flush_kernel_dcache_page before unmapping the
local mapping.  flush_kernel_dcache_page is required for all pages
potentially mapped into userspace that were written to using kmap*,
so having a helper that does the right thing can be very convenient.

Signed-off-by: Christoph Hellwig <hch@....de>
---
 include/linux/highmem-internal.h | 7 +++++++
 include/linux/highmem.h          | 4 ++++
 2 files changed, 11 insertions(+)

diff --git a/include/linux/highmem-internal.h b/include/linux/highmem-internal.h
index 7902c7d8b55f..bd37706db147 100644
--- a/include/linux/highmem-internal.h
+++ b/include/linux/highmem-internal.h
@@ -224,4 +224,11 @@ do {								\
 	__kunmap_local(__addr);					\
 } while (0)
 
+#define kunmap_local_dirty(__page, __addr)			\
+do {								\
+	if (!PageSlab(__page))					\
+		flush_kernel_dcache_page(__page);		\
+	kunmap_local(__addr);					\
+} while (0)
+
 #endif
diff --git a/include/linux/highmem.h b/include/linux/highmem.h
index 832b49b50c7b..65f548db4f2d 100644
--- a/include/linux/highmem.h
+++ b/include/linux/highmem.h
@@ -93,6 +93,10 @@ static inline void kmap_flush_unused(void);
  * On HIGHMEM enabled systems mapping a highmem page has the side effect of
  * disabling migration in order to keep the virtual address stable across
  * preemption. No caller of kmap_local_page() can rely on this side effect.
+ *
+ * If data is written to the returned kernel mapping, the callers needs to
+ * unmap the mapping using kunmap_local_dirty(), else kunmap_local() should
+ * be used.
  */
 static inline void *kmap_local_page(struct page *page);
 
-- 
2.30.2