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AKwUvByPRWfddxD+h8pzotgng90feyrAK1IvxMJXfa9wBa5yr11Ast2ZNPUowNukm/n+I/vRNL5PMoGQ50+3Kac=@vger.kernel.org X-Gm-Message-State: AFq9FYIh1o1sOf8ckfYy5+SS2wM/hOp9OIpMsaDe8vNDbSD8W9tpmcnm E9sMuswShCeLlLBA2+iJ1rc/N2I13dF1rFcQGOA1RYtGRC6rntw0il6El+oCMPJDfrP59BoTK3J z1scFLd5Lz/wBFA== X-Received: from dycmb19-n1.prod.google.com ([2002:a05:693c:20d3:10b0:351:731f:c917]) (user=digonzal job=prod-delivery.src-stubby-dispatcher) by 2002:a05:7300:bf9c:b0:34d:755b:d60b with SMTP id 5a478bee46e88-3674de4e3c1mr32887eec.34.1792519867908; Tue, 20 Oct 2026 11:11:07 -0700 (PDT) Date: Tue, 20 Oct 2026 18:10:52 +0000 X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list Mime-Version: 1.0 X-Mailer: git-send-email 2.56.0.218.g1ec904b173-goog Message-ID: <20261020181053.2646782-1-digonzal@google.com> Subject: [PATCH] PCI/ATS: Disable ATS when ACS TB is set upstream From: Danny Gonzalez To: Bjorn Helgaas Cc: David Decotigny , Sheena Mohan , linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org, Danny Gonzalez Content-Type: text/plain; charset="UTF-8" Enabling ATS allows an endpoint to cache translations and initiate DMA requests with Translated addresses, which an upstream bridge with ACS Translation Blocking (PCI_ACS_TB) set will block as ACS Violations. Because pci_enable_acs() preserves existing PCI_ACS_CTRL bits (e.g., from firmware, a kexec kernel, or "pci=config_acs=") without relaxing them, PCI_ACS_TB may remain set on upstream bridges. Update pci_ats_supported() to walk upstream bridges and return false if any bridge has PCI_ACS_TB set, leaving the endpoint to use Untranslated addresses. Tested by booting a machine with an endpoint advertising the ATS Capability behind a Root Port with PCI_ACS_TB set; verified ATS is disabled and the system boots cleanly. Signed-off-by: Danny Gonzalez --- drivers/pci/ats.c | 28 ++++++++++++++++++++++++++++ 1 file changed, 28 insertions(+) diff --git a/drivers/pci/ats.c b/drivers/pci/ats.c index 9cb23780093d..094f4f825acf 100644 --- a/drivers/pci/ats.c +++ b/drivers/pci/ats.c @@ -31,6 +31,24 @@ void pci_ats_init(struct pci_dev *dev) dev->ats_cap = pos; } +static struct pci_dev *pci_acs_tb_path_blocked(struct pci_dev *dev) +{ + struct pci_dev *bridge; + + for (bridge = pci_upstream_bridge(dev); bridge; + bridge = pci_upstream_bridge(bridge)) { + u16 ctrl; + + if (!bridge->acs_cap) + continue; + pci_read_config_word(bridge, bridge->acs_cap + PCI_ACS_CTRL, + &ctrl); + if (ctrl & PCI_ACS_TB) + return bridge; + } + return NULL; +} + /** * pci_ats_supported - check if the device can use ATS * @dev: the PCI device @@ -40,12 +58,22 @@ void pci_ats_init(struct pci_dev *dev) */ bool pci_ats_supported(struct pci_dev *dev) { + struct pci_dev *bridge; + if (!dev->ats_cap || dev->untrusted) return false; if (dev->is_virtfn) return pci_ats_supported(pci_physfn(dev)); + /* Do not allow ATS if any upstream bridge blocks translation */ + bridge = pci_acs_tb_path_blocked(dev); + if (bridge) { + pci_warn_once(dev, "ATS disabled: upstream bridge %s has ACS Translation Blocking enabled\n", + pci_name(bridge)); + return false; + } + return true; } EXPORT_SYMBOL_GPL(pci_ats_supported); -- 2.56.0.218.g1ec904b173-goog