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[79.182.31.92]) by smtp.gmail.com with ESMTPSA id d63sm8905146wmc.22.2020.07.01.14.23.33 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 01 Jul 2020 14:23:35 -0700 (PDT) Date: Wed, 1 Jul 2020 17:23:32 -0400 From: "Michael S. Tsirkin" To: Stefano Stabellini Cc: Christoph Hellwig , jgross@suse.com, Peng Fan , x86@kernel.org, konrad.wilk@oracle.com, jasowang@redhat.com, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, iommu@lists.linux-foundation.org, linux-imx@nxp.com, xen-devel@lists.xenproject.org, boris.ostrovsky@oracle.com, linux-arm-kernel@lists.infradead.org Subject: Re: [PATCH] xen: introduce xen_vring_use_dma Message-ID: <20200701172219-mutt-send-email-mst@kernel.org> References: <20200624050355-mutt-send-email-mst@kernel.org> <20200624163940-mutt-send-email-mst@kernel.org> <20200624181026-mutt-send-email-mst@kernel.org> <20200626110629-mutt-send-email-mst@kernel.org> <20200701133456.GA23888@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 01, 2020 at 10:34:53AM -0700, Stefano Stabellini wrote: > Would you be in favor of a more flexible check along the lines of the > one proposed in the patch that started this thread: > > if (xen_vring_use_dma()) > return true; > > > xen_vring_use_dma would be implemented so that it returns true when > xen_swiotlb is required and false otherwise. Just to stress - with a patch like this virtio can *still* use DMA API if PLATFORM_ACCESS is set. So if DMA API is broken on some platforms as you seem to be saying, you guys should fix it before doing something like this.. -- MST