From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jean-philippe Brucker Subject: Re: [PATCH v3 3/7] PCI: OF: Allow endpoints to bypass the iommu Date: Mon, 15 Oct 2018 20:45:47 +0100 Message-ID: <6abc7321-c46a-5618-1ce7-4be85fcc38ec@gmail.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" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20181012194158.GX5906-1RhO1Y9PlrlHTL0Zs8A6p5iNqAH0jzoTYJqu5kTmcBRl57MIdRCFDg@public.gmane.org> Content-Language: en-US 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 Cc: Mark Rutland , "peter.maydell-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org" , "kevin.tian-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org" , "tnowicki-M3mlKVOIwJVv6pq1l3V1OdBPR1lH4CV8@public.gmane.org" , "devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "jasowang-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org" , "linux-pci-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "mst-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org" , Will Deacon , "virtualization-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org" , "iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org" , "robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org" , jean-philippe.brucker-5wv7dgnIgG8@public.gmane.org, Marc Zyngier , Robin Murphy , "kvmarm-FPEHb7Xf0XXUo1n7N8X6UoWGPAHP3yOg@public.gmane.org" List-Id: devicetree@vger.kernel.org [Replying with my personal address because we're having SMTP issues] On 12/10/2018 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? As Robin said, a device that is absent from iommu-map will be ignored by the IOMMU layer, so it depends on the specific IOMMU implementation and driver. By default the SMMU and virtio-iommu drivers disable bypass, but I'm not sure about the others. I'll try to find a more accurate title for this patch > Should we > indicate something in dmesg (and/or sysfs) about devices that bypass > it? Good idea, I'll replace the pr_err() below with a pr_info(), instead of simply removing it. >> Relaxing of_pci_map_rid also allows the msi-map property to have gaps, > > 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. Right, I'll clarify this. It's pci_msi_setup_msi_irqs() that returns an error if the device is missing from msi-map, so the device driver won't be able to request MSIs. Thanks, Jean >> 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 >> >