linux-kernel - Re: [PATCH 1/2] mm: call flush_dcache_page in memcpy_to_page and memzero

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Message-ID: <20210714052841.GA6380@lst.de>
Date:   Wed, 14 Jul 2021 07:28:41 +0200
From:   Christoph Hellwig <hch@....de>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Christoph Hellwig <hch@....de>, Ira Weiny <ira.weiny@...el.com>,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 1/2] mm: call flush_dcache_page in memcpy_to_page and
 memzero_page

On Tue, Jul 13, 2021 at 06:31:23PM -0700, Andrew Morton wrote:
> On Tue, 13 Jul 2021 07:52:30 +0200 Christoph Hellwig <hch@....de> wrote:
> 
> > memcpy_to_page and memzero_page can write to arbitrary pages, which could
> > be in the page cache or in high memory, so  call flush_kernel_dcache_pages
> > to flush the dcache.
> 
> I assume this presently is not known to cause any problems, but that
> some problems might be discovered in the future?  In which case,
> should we cc:stable?

This is a problem when using these helpers on dcache challeneged
architectures.  Right now there are just a few users, chances
are no one used the PC floppy drіver, the aha1542 driver for an ISA
SCSI HBA, and a few advanced and optional btrfs and ext4 features
on those platforms yet since the conversion.  So yes, stable would be
good.