Re: [04/26] ARM: 7755/1: handle user space mapped pages in flush_kernel_dcache_page

[Luis Henriques <luis.henriques@canonical.com>]

Ben Hutchings <ben@decadent.org.uk> writes:

> 3.2.48-rc1 review patch.  If anyone has any objections, please let me know.
>
> ------------------
>
> From: Simon Baatz <gmbnomis@gmail.com>
>
> commit 1bc39742aab09248169ef9d3727c9def3528b3f3 upstream.

Simon suggested Greg not to queue this patch for stable kernels as it
breaks no-MMU ARM configs.  He will provide a follow-up patch that
should go together with this one.

Cheers,
-- 
Luis

>
> Commit f8b63c1 made flush_kernel_dcache_page a no-op assuming that
> the pages it needs to handle are kernel mapped only.  However, for
> example when doing direct I/O, pages with user space mappings may
> occur.
>
> Thus, continue to do lazy flushing if there are no user space
> mappings.  Otherwise, flush the kernel cache lines directly.
>
> Signed-off-by: Simon Baatz <gmbnomis@gmail.com>
> Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
> Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
> Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
> ---
>  arch/arm/include/asm/cacheflush.h |    4 +---
>  arch/arm/mm/flush.c               |   33 +++++++++++++++++++++++++++++++++
>  2 files changed, 34 insertions(+), 3 deletions(-)
>
> --- a/arch/arm/include/asm/cacheflush.h
> +++ b/arch/arm/include/asm/cacheflush.h
> @@ -301,9 +301,7 @@ static inline void flush_anon_page(struc
>  }
>  
>  #define ARCH_HAS_FLUSH_KERNEL_DCACHE_PAGE
> -static inline void flush_kernel_dcache_page(struct page *page)
> -{
> -}
> +extern void flush_kernel_dcache_page(struct page *);
>  
>  #define flush_dcache_mmap_lock(mapping) \
>  	spin_lock_irq(&(mapping)->tree_lock)
> --- a/arch/arm/mm/flush.c
> +++ b/arch/arm/mm/flush.c
> @@ -304,6 +304,39 @@ void flush_dcache_page(struct page *page
>  EXPORT_SYMBOL(flush_dcache_page);
>  
>  /*
> + * Ensure cache coherency for the kernel mapping of this page. We can
> + * assume that the page is pinned via kmap.
> + *
> + * If the page only exists in the page cache and there are no user
> + * space mappings, this is a no-op since the page was already marked
> + * dirty at creation.  Otherwise, we need to flush the dirty kernel
> + * cache lines directly.
> + */
> +void flush_kernel_dcache_page(struct page *page)
> +{
> +	if (cache_is_vivt() || cache_is_vipt_aliasing()) {
> +		struct address_space *mapping;
> +
> +		mapping = page_mapping(page);
> +
> +		if (!mapping || mapping_mapped(mapping)) {
> +			void *addr;
> +
> +			addr = page_address(page);
> +			/*
> +			 * kmap_atomic() doesn't set the page virtual
> +			 * address for highmem pages, and
> +			 * kunmap_atomic() takes care of cache
> +			 * flushing already.
> +			 */
> +			if (!IS_ENABLED(CONFIG_HIGHMEM) || addr)
> +				__cpuc_flush_dcache_area(addr, PAGE_SIZE);
> +		}
> +	}
> +}
> +EXPORT_SYMBOL(flush_kernel_dcache_page);
> +
> +/*
>   * Flush an anonymous page so that users of get_user_pages()
>   * can safely access the data.  The expected sequence is:
>   *
>
> --
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