linux-kernel - Re: [PATCH] mm: D-cache aliasing issue in cow_user

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Date:	Tue, 05 Dec 2006 13:24:12 -0800 (PST)
From:	David Miller <davem@...emloft.net>
To:	mattjreimer@...il.com
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm: D-cache aliasing issue in cow_user_page

From: "Matt Reimer" <mattjreimer@...il.com>
Date: Mon, 4 Dec 2006 23:38:13 -0800

> In light of James Bottomsley's commit[1] declaring that kmap() and
> friends now have to take care of coherency issues, is the patch "mm:
> D-cache aliasing issue in cow_user_page"[2] correct, or could it
> potentially cause a slowdown by calling flush_dcache_page() a second
> time (i.e. once in an architecture-specific kmap() implementation, and
> once in cow_user_page())?

kmap() is a NOP unless HIGHMEM is configured.

Therefore, it cannot possibly take care of D-cache aliasing issues
across the board.
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