linux-kernel - Re: [PATCH v2] powerpc: warn on emulation of dcbz instruction in kernel mode

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Message-ID: <20240822053238.GA2028@lst.de>
Date: Thu, 22 Aug 2024 07:32:38 +0200
From: Christoph Hellwig <hch@....de>
To: LEROY Christophe <christophe.leroy2@...soprasteria.com>
Cc: Christian Lamparter <christian.lamparter@....uni-stuttgart.de>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
	Stan Johnson <userm57@...oo.com>,
	Finn Thain <fthain@...ux-m68k.org>, Christoph Hellwig <hch@....de>
Subject: Re: [PATCH v2] powerpc: warn on emulation of dcbz instruction in
 kernel mode

On Thu, Aug 22, 2024 at 05:25:10AM +0000, LEROY Christophe wrote:
> > and this results in a call to dma_direct_allocation(), which has one
> > innocent looking memset():
> 
> 
> memset() can't be used on non-cached memory, memset_io() has to be used
> instead.

No, we use memset on uncached memory all the time.  Note that uncached
memory != __iomem memory, for which you DO have to use memset_io.