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Date: Tue, 21 May 2024 12:49:39 -0300
From: Jason Gunthorpe <jgg@nvidia.com>
To: Christoph Hellwig <hch@infradead.org>
Cc: Yan Zhao <yan.y.zhao@intel.com>, kvm@vger.kernel.org,
	linux-kernel@vger.kernel.org, x86@kernel.org,
	alex.williamson@redhat.com, kevin.tian@intel.com,
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	dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org,
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	robin.murphy@arm.com, baolu.lu@linux.intel.com, yi.l.liu@intel.com,
	Russell King <linux@armlinux.org.uk>
Subject: Re: [PATCH 3/5] x86/mm: Introduce and export interface
 arch_clean_nonsnoop_dma()
Message-ID: <20240521154939.GH20229@nvidia.com>
References: <20240507061802.20184-1-yan.y.zhao@intel.com>
 <20240507062044.20399-1-yan.y.zhao@intel.com>
 <ZktZDmcNnsHhp4Tm@infradead.org>
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On Mon, May 20, 2024 at 07:07:10AM -0700, Christoph Hellwig wrote:
> On Tue, May 07, 2024 at 02:20:44PM +0800, Yan Zhao wrote:
> > Introduce and export interface arch_clean_nonsnoop_dma() to flush CPU
> > caches for memory involved in non-coherent DMAs (DMAs that lack CPU cache
> > snooping).
> 
> Err, no.  There should really be no exported cache manipulation macros,
> as drivers are almost guaranteed to get this wrong.  I've added
> Russell to the Cc list who has been extremtly vocal about this at least
> for arm.

We could possibly move this under some IOMMU core API (ie flush and
map, unmap and flush), the iommu APIs are non-modular so this could
avoid the exported symbol.

Jason