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Wysocki" , Len Brown , iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org, linux-acpi@vger.kernel.org, Raj Ashok , lalithambika.krishnakumar@intel.com, Mika Westerberg , Jean-Philippe Brucker , Prashant Malani , Benson Leung , Todd Broch , Alex Levin , Mattias Nissler , Rajat Jain , Bernie Keany , Aaron Durbin , Diego Rivas , Duncan Laurie , Furquan Shaikh , Jesse Barnes , Christian Kellner , Alex Williamson , Greg Kroah-Hartman , oohall@gmail.com Cc: Rajat Jain X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , From: Rajat Jain via iommu Reply-To: Rajat Jain Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" Introduce a PCI parameter that disables the automatic attachment of untrusted devices to their drivers. Signed-off-by: Rajat Jain --- Context: I set out to implement the approach outlined in https://lkml.org/lkml/2020/6/9/1331 https://lkml.org/lkml/2020/6/15/1453 But to my surprise, I found that the new hotplugged PCI devices were getting automatically attached to drivers even though /sys/bus/pci/drivers_autoprobe was set to 0. I realized that the device core's "drivers_autoprobe": * only disables the *initial* probe of the device (i.e. from device_add()). If a subsystem calls device_attach() explicitly for its devices like PCI subsystem does, the drivers_autoprobe setting does not matter. The core will attach device to the driver. This looks like correct semantic behavior to me because PCI is explicitly calling device_attach(), which is a way to explicitly ask the core to find and attach a driver for a device. * "drivers_autoprobe" cannot be controlled at boot time (to restrict any drivers before userspace comes up). The options I considered were: 1) Change device_attach() so that it takes into consideration the drivers_autoprobe property. Not sure if this is semantically correct thing to do though. If I do this, then the only way a driver can be attached to the drivers would be via userspace (/sys/bus/pci/drivers/bind) (Good for our use case though!). 2) Make the drivers_autoprobe property available to PCI to use (currently it is private to device core). The PCI could use this to determine whether or not to call device_attach(). This still leaves the other problem (of not being able to set drivers_autoprobe via command line open). 3) I found the pci_dev->match_driver, which seemed similar to what I am trying to do, but can't be controlled from userspace. I considered populating that field based on drivers_autoprobe (still need (2)). But the problem is that there is the AMD IOMMU driver which is setting this independently, so setting the match_driver based on drivers_autoprobe may not be a good idea. May be we can populate it for untrusted devicesi, based on the parameter that I'm introducing? 4) This patch was my option 4 that helps fix both the problems for me. drivers/pci/bus.c | 11 ++++++++--- drivers/pci/pci.c | 9 +++++++++ drivers/pci/pci.h | 1 + 3 files changed, 18 insertions(+), 3 deletions(-) diff --git a/drivers/pci/bus.c b/drivers/pci/bus.c index 3cef835b375fd..336aeeb4c4ebf 100644 --- a/drivers/pci/bus.c +++ b/drivers/pci/bus.c @@ -321,9 +321,14 @@ void pci_bus_add_device(struct pci_dev *dev) pci_bridge_d3_update(dev); dev->match_driver = true; - retval = device_attach(&dev->dev); - if (retval < 0 && retval != -EPROBE_DEFER) - pci_warn(dev, "device attach failed (%d)\n", retval); + + if (dev->untrusted && pci_dont_attach_untrusted_devs) { + pci_info(dev, "not attaching untrusted device\n"); + } else { + retval = device_attach(&dev->dev); + if (retval < 0 && retval != -EPROBE_DEFER) + pci_warn(dev, "device attach failed (%d)\n", retval); + } pci_dev_assign_added(dev, true); } diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c index ce096272f52b1..dec1f9ef27d71 100644 --- a/drivers/pci/pci.c +++ b/drivers/pci/pci.c @@ -127,6 +127,13 @@ static bool pcie_ats_disabled; /* If set, the PCI config space of each device is printed during boot. */ bool pci_early_dump; +/* + * If set, the devices with "untrusted" flag shall not be attached automatically + * Userspace will need to attach them manually: + * echo > /sys/bus/pci/drivers//bind + */ +bool pci_dont_attach_untrusted_devs; + bool pci_ats_disabled(void) { return pcie_ats_disabled; @@ -6522,6 +6529,8 @@ static int __init pci_setup(char *str) pci_add_flags(PCI_SCAN_ALL_PCIE_DEVS); } else if (!strncmp(str, "disable_acs_redir=", 18)) { disable_acs_redir_param = str + 18; + } else if (!strcmp(str, "dont_attach_untrusted_devs")) { + pci_dont_attach_untrusted_devs = true; } else { pr_err("PCI: Unknown option `%s'\n", str); } diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h index 6d3f758671064..30ffad047d926 100644 --- a/drivers/pci/pci.h +++ b/drivers/pci/pci.h @@ -13,6 +13,7 @@ extern const unsigned char pcie_link_speed[]; extern bool pci_early_dump; +extern bool pci_dont_attach_untrusted_devs; bool pcie_cap_has_lnkctl(const struct pci_dev *dev); bool pcie_cap_has_rtctl(const struct pci_dev *dev); -- 2.27.0.212.ge8ba1cc988-goog _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu