linux-kernel - Re: flush_dcache_page vs kunmap

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Message-ID: <YYQkdUcSLFPlzGFH@shell.armlinux.org.uk>
Date:   Thu, 4 Nov 2021 18:20:37 +0000
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>,
        Christoph Hellwig <hch@....de>,
        linux-arch <linux-arch@...r.kernel.org>,
        Ira Weiny <ira.weiny@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: flush_dcache_page vs kunmap_local

On Thu, Nov 04, 2021 at 06:04:45PM +0000, Catalin Marinas wrote:
> The cachetlb.rst doc states the two cases where flush_dcache_page()
> should be called:
> 
> 1. After writing to a page cache page (that's what we need on arm64 for
>    the I-cache).
> 
> 2. Before reading from a page cache page and user mappings potentially
>    exist. I think arm32 ensures the D-cache user aliases are coherent
>    with the kernel one (added rmk to confirm).

Yes, where necessary, we flush the user aliases in flush_dcache_page().

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