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    Subject[PATCH 01/18] mm: add a kunmap_local_dirty helper
    Date
    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@lst.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
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