From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Michael S. Tsirkin" Subject: Re: [PATCH v3 3/7] PCI: OF: Allow endpoints to bypass the iommu Date: Mon, 15 Oct 2018 06:52:10 -0400 Message-ID: <20181015065024-mutt-send-email-mst@kernel.org> 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: Content-Disposition: inline In-Reply-To: <20181012194158.GX5906-1RhO1Y9PlrlHTL0Zs8A6p5iNqAH0jzoTYJqu5kTmcBRl57MIdRCFDg@public.gmane.org> 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-5wv7dgnIgG8@public.gmane.org, devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, kevin.tian-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org, tnowicki-M3mlKVOIwJVv6pq1l3V1OdBPR1lH4CV8@public.gmane.org, peter.maydell-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org, Jean-Philippe Brucker , linux-pci-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, will.deacon-5wv7dgnIgG8@public.gmane.org, robin.murphy-5wv7dgnIgG8@public.gmane.org, virtualization-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, iommu-cunTk1MwBs9QetFLy7KEm3xJsTq8ys+cHZ5vskTnxNA@public.gmane.org, robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org, marc.zyngier-5wv7dgnIgG8@public.gmane.org, jasowang-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org, kvmarm-FPEHb7Xf0XXUo1n7N8X6UoWGPAHP3yOg@public.gmane.org List-Id: devicetree@vger.kernel.org On Fri, Oct 12, 2018 at 02:41:59PM -0500, 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? Thinking about this comment, I would like to ask: can't the virtio device indicate the ranges in a portable way? This would minimize the dependency on dt bindings and ACPI, enabling support for systems that have neither but do have virtio e.g. through pci. > Should we > indicate something in dmesg (and/or sysfs) about devices that bypass > 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. > > > 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 > >