From 462b58fb033996e999cc213ed0b430d4f22a28fe Mon Sep 17 00:00:00 2001 From: Rajat Jain Date: Wed, 28 Oct 2020 16:15:45 -0700 Subject: [PATCH] PCI: Always enable ACS even if no ACS Capability Some devices support ACS functionality even though they don't have a spec-compliant ACS Capability; pci_enable_acs() has a quirk mechanism to handle them. We want to enable ACS whenever possible, but 52fbf5bdeeef ("PCI: Cache ACS capability offset in device") inadvertently broke this by calling pci_enable_acs() only if we find an ACS Capability. This resulted in ACS not being enabled for these non-compliant devices, which means devices can't be separated into different IOMMU groups, which in turn means we may not be able to pass those devices through to VMs, as reported by Boris V: https://lore.kernel.org/r/74aeea93-8a46-5f5a-343c-790d4c655da3@bstnet.org Fixes: 52fbf5bdeeef ("PCI: Cache ACS capability offset in device") Link: https://lore.kernel.org/r/20201028231545.4116866-1-rajatja@google.com Reported-by: Boris V Signed-off-by: Rajat Jain Signed-off-by: Bjorn Helgaas Reviewed-by: Alex Williamson --- drivers/pci/pci.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c index 6d4d5a2f923d9..e578d34095e91 100644 --- a/drivers/pci/pci.c +++ b/drivers/pci/pci.c @@ -3516,8 +3516,13 @@ void pci_acs_init(struct pci_dev *dev) { dev->acs_cap = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_ACS); - if (dev->acs_cap) - pci_enable_acs(dev); + /* + * Attempt to enable ACS regardless of capability because some Root + * Ports (e.g. those quirked with *_intel_pch_acs_*) do not have + * the standard ACS capability but still support ACS via those + * quirks. + */ + pci_enable_acs(dev); } /** -- 2.30.2