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[79.176.28.95]) by smtp.gmail.com with ESMTPSA id c8sm216623qkk.37.2020.02.17.05.31.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 17 Feb 2020 05:31:53 -0800 (PST) Date: Mon, 17 Feb 2020 08:31:48 -0500 From: "Michael S. Tsirkin" To: Robin Murphy Cc: Jean-Philippe Brucker , iommu@lists.linux-foundation.org, virtualization@lists.linux-foundation.org, linux-pci@vger.kernel.org, kevin.tian@intel.com, sebastien.boeuf@intel.com, jacob.jun.pan@intel.com, bhelgaas@google.com, jasowang@redhat.com Subject: Re: [PATCH 3/3] iommu/virtio: Enable x86 support Message-ID: <20200217083112-mutt-send-email-mst@kernel.org> References: <20200214160413.1475396-1-jean-philippe@linaro.org> <20200214160413.1475396-4-jean-philippe@linaro.org> <311a1885-c619-3c8d-29dd-14fbfbf74898@arm.com> <20200216045006-mutt-send-email-mst@kernel.org> <20200217090107.GA1650092@myrica> <20200217080129-mutt-send-email-mst@kernel.org> <915044ae-6972-e0eb-43e8-d071af848fe3@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <915044ae-6972-e0eb-43e8-d071af848fe3@arm.com> Sender: linux-pci-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org On Mon, Feb 17, 2020 at 01:22:44PM +0000, Robin Murphy wrote: > On 17/02/2020 1:01 pm, Michael S. Tsirkin wrote: > > On Mon, Feb 17, 2020 at 10:01:07AM +0100, Jean-Philippe Brucker wrote: > > > On Sun, Feb 16, 2020 at 04:50:33AM -0500, Michael S. Tsirkin wrote: > > > > On Fri, Feb 14, 2020 at 04:57:11PM +0000, Robin Murphy wrote: > > > > > On 14/02/2020 4:04 pm, Jean-Philippe Brucker wrote: > > > > > > With the built-in topology description in place, x86 platforms can now > > > > > > use the virtio-iommu. > > > > > > > > > > > > Signed-off-by: Jean-Philippe Brucker > > > > > > --- > > > > > > drivers/iommu/Kconfig | 3 ++- > > > > > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > > > > > > > > > diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig > > > > > > index 068d4e0e3541..adcbda44d473 100644 > > > > > > --- a/drivers/iommu/Kconfig > > > > > > +++ b/drivers/iommu/Kconfig > > > > > > @@ -508,8 +508,9 @@ config HYPERV_IOMMU > > > > > > config VIRTIO_IOMMU > > > > > > bool "Virtio IOMMU driver" > > > > > > depends on VIRTIO=y > > > > > > - depends on ARM64 > > > > > > + depends on (ARM64 || X86) > > > > > > select IOMMU_API > > > > > > + select IOMMU_DMA > > > > > > > > > > Can that have an "if X86" for clarity? AIUI it's not necessary for > > > > > virtio-iommu itself (and really shouldn't be), but is merely to satisfy the > > > > > x86 arch code's expectation that IOMMU drivers bring their own DMA ops, > > > > > right? > > > > > > > > > > Robin. > > > > > > > > In fact does not this work on any platform now? > > > > > > There is ongoing work to use the generic IOMMU_DMA ops on X86. AMD IOMMU > > > has been converted recently [1] but VT-d still implements its own DMA ops > > > (conversion patches are on the list [2]). On Arm the arch Kconfig selects > > > IOMMU_DMA, and I assume we'll have the same on X86 once Tom's work is > > > complete. Until then I can add a "if X86" here for clarity. > > > > > > Thanks, > > > Jean > > > > > > [1] https://lore.kernel.org/linux-iommu/20190613223901.9523-1-murphyt7@tcd.ie/ > > > [2] https://lore.kernel.org/linux-iommu/20191221150402.13868-1-murphyt7@tcd.ie/ > > > > What about others? E.g. PPC? > > That was the point I was getting at - while iommu-dma should build just fine > for the likes of PPC, s390, 32-bit Arm, etc., they have no architecture code > to correctly wire up iommu_dma_ops to devices. Thus there's currently no > point pulling it in and pretending it's anything more than a waste of space > for architectures other than arm64 and x86. It's merely a historical > artefact of the x86 DMA API implementation that when the IOMMU drivers were > split out to form drivers/iommu they took some of their relevant arch code > with them. > > Robin. Rather than white-listing architectures, how about making the architectures in question set some kind of symbol, and depend on it? -- MST