From mboxrd@z Thu Jan 1 00:00:00 1970 From: Robin Murphy Subject: Re: [PATCH v3 3/7] PCI: OF: Allow endpoints to bypass the iommu Date: Mon, 15 Oct 2018 12:32:51 +0100 Message-ID: <33bd48e9-a061-e97d-ff00-daf5097b8e1f@arm.com> References: <20181012145917.6840-1-jean-philippe.brucker@arm.com> <20181012145917.6840-4-jean-philippe.brucker@arm.com> <20181012194158.GX5906@bhelgaas-glaptop.roam.corp.google.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20181012194158.GX5906-1RhO1Y9PlrlHTL0Zs8A6p5iNqAH0jzoTYJqu5kTmcBRl57MIdRCFDg@public.gmane.org> Content-Language: en-GB List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org Errors-To: iommu-bounces-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org To: Bjorn Helgaas , Jean-Philippe Brucker Cc: mark.rutland-5wv7dgnIgG8@public.gmane.org, peter.maydell-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org, kevin.tian-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org, tnowicki-M3mlKVOIwJVv6pq1l3V1OdBPR1lH4CV8@public.gmane.org, devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, marc.zyngier-5wv7dgnIgG8@public.gmane.org, linux-pci-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, jasowang-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, mst-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, will.deacon-5wv7dgnIgG8@public.gmane.org, virtualization-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.orgnd-5wv7dgnIgG8@public.gmane.org, kvmarm-FPEHb7Xf0XXUo1n7N8X6UoWGPAHP3yOg@public.gmane.org List-Id: devicetree@vger.kernel.org On 12/10/18 20:41, Bjorn Helgaas wrote: > s/iommu/IOMMU/ in subject > > On Fri, Oct 12, 2018 at 03:59:13PM +0100, Jean-Philippe Brucker wrote: >> Using the iommu-map binding, endpoints in a given PCI domain can be >> managed by different IOMMUs. Some virtual machines may allow a subset of >> endpoints to bypass the IOMMU. In some case the IOMMU itself is presented > > s/case/cases/ > >> as a PCI endpoint (e.g. AMD IOMMU and virtio-iommu). Currently, when a >> PCI root complex has an iommu-map property, the driver requires all >> endpoints to be described by the property. Allow the iommu-map property to >> have gaps. > > I'm not an IOMMU or virtio expert, so it's not obvious to me why it is > safe to allow devices to bypass the IOMMU. Does this mean a typo in > iommu-map could inadvertently allow devices to bypass it? Should we > indicate something in dmesg (and/or sysfs) about devices that bypass > it? It's not really "allow devices to bypass the IOMMU" so much as "allow DT to describe devices which the IOMMU doesn't translate". It's a bit of an edge case for not-really-PCI devices, but FWIW I can certainly think of several ways to build real hardware like that. As for inadvertent errors leaving out IDs which *should* be in the map, that really depends on the IOMMU/driver implementation - e.g. SMMUv2 with arm-smmu.disable_bypass=0 would treat the device as untranslated, whereas SMMUv3 would always generate a fault upon any transaction due to no valid stream table entry being programmed (not even a bypass one). I reckon it's a sufficiently unusual case that keeping some sort of message probably is worthwhile (at pr_info rather than pr_err) in case someone does hit it by mistake. >> Relaxing of_pci_map_rid also allows the msi-map property to have gaps, At worst, I suppose we could always add yet another parameter for each caller to choose whether a missing entry is considered an error or not. Robin. > s/of_pci_map_rid/of_pci_map_rid()/ > >> which is invalid since MSIs always reach an MSI controller. Thankfully >> Linux will error out later, when attempting to find an MSI domain for the >> device. > > Not clear to me what "error out" means here. In a userspace program, > I would infer that the program exits with an error message, but I > doubt you mean that Linux exits. > >> Signed-off-by: Jean-Philippe Brucker >> --- >> drivers/pci/of.c | 7 ++++--- >> 1 file changed, 4 insertions(+), 3 deletions(-) >> >> diff --git a/drivers/pci/of.c b/drivers/pci/of.c >> index 1836b8ddf292..2f5015bdb256 100644 >> --- a/drivers/pci/of.c >> +++ b/drivers/pci/of.c >> @@ -451,9 +451,10 @@ int of_pci_map_rid(struct device_node *np, u32 rid, >> return 0; >> } >> >> - pr_err("%pOF: Invalid %s translation - no match for rid 0x%x on %pOF\n", >> - np, map_name, rid, target && *target ? *target : NULL); >> - return -EFAULT; >> + /* Bypasses translation */ >> + if (id_out) >> + *id_out = rid; >> + return 0; >> } >> >> #if IS_ENABLED(CONFIG_OF_IRQ) >> -- >> 2.19.1 >> > _______________________________________________ > iommu mailing list > iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org > https://lists.linuxfoundation.org/mailman/listinfo/iommu >