Received-SPF: pass (google.com: domain of linux-kernel+bounces-191814-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:4601:e00::3 as permitted sender) client-ip=2604:1380:4601:e00::3;
Date: Mon, 27 May 2024 23:37:34 -0700
From: Christoph Hellwig <hch@infradead.org>
To: Jason Gunthorpe <jgg@nvidia.com>
Cc: Christoph Hellwig <hch@infradead.org>, 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,
	iommu@lists.linux.dev, pbonzini@redhat.com, seanjc@google.com,
	dave.hansen@linux.intel.com, luto@kernel.org, peterz@infradead.org,
	tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, hpa@zytor.com,
	corbet@lwn.net, joro@8bytes.org, will@kernel.org,
	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: <ZlV7rlmWdU7dJZKo@infradead.org>
References: <20240507061802.20184-1-yan.y.zhao@intel.com>
 <20240507062044.20399-1-yan.y.zhao@intel.com>
 <ZktZDmcNnsHhp4Tm@infradead.org>
 <20240521154939.GH20229@nvidia.com>
 <20240521160016.GA2513156@nvidia.com>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20240521160016.GA2513156@nvidia.com>

On Tue, May 21, 2024 at 01:00:16PM -0300, Jason Gunthorpe wrote:
> > > 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.
> 
> Though this would be pretty difficult for unmap as we don't have the
> pfns in the core code to flush. I don't think we have alot of good
> options but to make iommufd & VFIO handle this directly as they have
> the list of pages to flush on the unmap side. Use a namespace?

Just have a unmap version that also takes a list of PFNs that you'd
need for non-coherent mappings?