linux-kernel - Re: [PATCH 3/4] MIPS: Handle highmem pages in __update

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Date:	Tue, 29 Mar 2016 10:39:54 +0200
From:	Ralf Baechle <ralf@...ux-mips.org>
To:	Paul Burton <paul.burton@...tec.com>
Cc:	linux-mips@...ux-mips.org, Lars Persson <lars.persson@...s.com>,
	"stable # v4 . 1+" <stable@...r.kernel.org>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jerome Marchand <jmarchan@...hat.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH 3/4] MIPS: Handle highmem pages in __update_cache

On Tue, Mar 01, 2016 at 02:37:58AM +0000, Paul Burton wrote:

> The following patch will expose __update_cache to highmem pages. Handle
> them by mapping them in for the duration of the cache maintenance, just
> like in __flush_dcache_page. The code for that isn't shared because we
> need the page address in __update_cache so sharing became messy. Given
> that the entirity is an extra 5 lines, just duplicate it.
> 
> Signed-off-by: Paul Burton <paul.burton@...tec.com>
> Cc: Lars Persson <lars.persson@...s.com>
> Cc: stable <stable@...r.kernel.org> # v4.1+
> ---
> 
>  arch/mips/mm/cache.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/mips/mm/cache.c b/arch/mips/mm/cache.c
> index 5a67d8c..8befa55 100644
> --- a/arch/mips/mm/cache.c
> +++ b/arch/mips/mm/cache.c
> @@ -149,9 +149,17 @@ void __update_cache(struct vm_area_struct *vma, unsigned long address,
>  		return;
>  	page = pfn_to_page(pfn);
>  	if (page_mapping(page) && Page_dcache_dirty(page)) {
> -		addr = (unsigned long) page_address(page);
> +		if (PageHighMem(page))
> +			addr = (unsigned long)kmap_atomic(page);
> +		else
> +			addr = (unsigned long)page_address(page);
> +
>  		if (exec || pages_do_alias(addr, address & PAGE_MASK))
>  			flush_data_cache_page(addr);
> +
> +		if (PageHighMem(page))
> +			__kunmap_atomic((void *)addr);
> +
>  		ClearPageDcacheDirty(page);
>  	}
>  }

Yet again this is betting the house on getting the right virtual address
from kmap_atomic.

  Ralf