On Wed, Nov 04, 2020 at 09:44:04AM +0100, Daniel Vetter wrote: > On Tue, Nov 3, 2020 at 11:09 PM Dan Williams <dan.j.williams@xxxxxxxxx> wrote: > > On Tue, Nov 3, 2020 at 1:28 PM Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote: > > > On Fri, Oct 30, 2020 at 11:08:11AM +0100, Daniel Vetter wrote: > > > > There's three ways to access PCI BARs from userspace: /dev/mem, sysfs > > > > files, and the old proc interface. Two check against > > > > iomem_is_exclusive, proc never did. And with CONFIG_IO_STRICT_DEVMEM, > > > > this starts to matter, since we don't want random userspace having > > > > access to PCI BARs while a driver is loaded and using it. > > > > > > > > Fix this by adding the same iomem_is_exclusive() check we already have > > > > on the sysfs side in pci_mmap_resource(). > > > > > > > > References: 90a545e98126 ("restrict /dev/mem to idle io memory ranges") > > > > Signed-off-by: Daniel Vetter <daniel.vetter@xxxxxxxxx> > > > > > > This is OK with me but it looks like IORESOURCE_EXCLUSIVE is currently > > > only used in a few places: > > > > > > e1000_probe() calls pci_request_selected_regions_exclusive(), > > > ne_pci_probe() calls pci_request_regions_exclusive(), > > > vmbus_allocate_mmio() calls request_mem_region_exclusive() > > > > > > which raises the question of whether it's worth keeping > > > IORESOURCE_EXCLUSIVE at all. I'm totally fine with removing it > > > completely. > > > > Now that CONFIG_IO_STRICT_DEVMEM upgrades IORESOURCE_BUSY to > > IORESOURCE_EXCLUSIVE semantics the latter has lost its meaning so I'd > > be in favor of removing it as well. > > Still has some value since it enforces exclusive access even if the > config isn't enabled, and iirc e1000 had some fun with userspace tools > clobbering the firmware and bricking the chip. There's *some* value; I'm just skeptical since only three drivers use it. IORESOURCE_EXCLUSIVE is from e8de1481fd71 ("resource: allow MMIO exclusivity for device drivers"), and the commit message says this is only active when CONFIG_STRICT_DEVMEM is set. I didn't check to see whether that's still true. That commit adds a bunch of wrappers and "__"-prefixed functions to pass the IORESOURCE_EXCLUSIVE flag around. That's a fair bit of uglification for three drivers. > Another thing I kinda wondered, since pci maintainer is here: At least > in drivers/gpu I see very few drivers explicitly requestion regions > (this might be a historical artifact due to the shadow attach stuff > before we had real modesetting drivers). And pci core doesn't do that > either, even when a driver is bound. Is this intentional, or > should/could we do better? Since drivers work happily without > reserving regions I don't think "the drivers need to remember to do > this" will ever really work out well. You're right, many drivers don't call pci_request_regions(). Maybe we could do better, but I haven't looked into that recently. There is a related note in Documentation/PCI/pci.rst that's been there for a long time (it refers to "pci_request_resources()", which has never existed AFAICT). I'm certainly open to proposals. _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel