linux-kernel - [PATCH] PCI/ACS: Enforce pci=noats with Transaction Blocking

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Message-ID: <162404966325.2362347.12176138291577486015.stgit@omen>
Date:   Fri, 18 Jun 2021 14:55:14 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     linux-pci@...r.kernel.org, bhelgaas@...gle.com
Cc:     rajatja@...gle.com, linux-kernel@...r.kernel.org
Subject: [PATCH] PCI/ACS: Enforce pci=noats with Transaction Blocking

PCIe Address Translation Services (ATS) provides a mechanism for a
device to provide an on-device caching translation agent (device
iotlb).  We already have a means to disable support for this feature
via the pci=noats option.  For untrusted and externally facing
devices, we not only disable ATS support for the device, but we use
Access Control Services (ACS) Transaction Blocking to actively
prevent devices from sending TLPs with non-default AT field values.

Extend pci=noats to also make use of PCI_ACS_TB so that not only is
ATS disabled at the device, but blocked at the downstream ports.
This provides a means to further lock-down ATS for cases such as
device assignment, where it may not be the hardware configuration of
the device that makes it untrusted, but the driver running on the
device.

Cc: Rajat Jain <rajatja@...gle.com>
Signed-off-by: Alex Williamson <alex.williamson@...hat.com>
---
 drivers/pci/pci.c    |    4 ++--
 drivers/pci/quirks.c |    2 +-
 2 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index 68f57d86b243..5aa1bb2ddd80 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -915,8 +915,8 @@ static void pci_std_enable_acs(struct pci_dev *dev)
 	/* Upstream Forwarding */
 	ctrl |= (cap & PCI_ACS_UF);

-	/* Enable Translation Blocking for external devices */
-	if (dev->external_facing || dev->untrusted)
+	/* Enable Translation Blocking for external devices and noats */
+	if (pci_ats_disabled() || dev->external_facing || dev->untrusted)
 		ctrl |= (cap & PCI_ACS_TB);

 	pci_write_config_word(dev, pos + PCI_ACS_CTRL, ctrl);
diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
index 6d74386eadc2..d541076c083a 100644
--- a/drivers/pci/quirks.c
+++ b/drivers/pci/quirks.c
@@ -5031,7 +5031,7 @@ static int pci_quirk_enable_intel_spt_pch_acs(struct pci_dev *dev)
 	ctrl |= (cap & PCI_ACS_CR);
 	ctrl |= (cap & PCI_ACS_UF);

-	if (dev->external_facing || dev->untrusted)
+	if (pci_ats_disabled() || dev->external_facing || dev->untrusted)
 		ctrl |= (cap & PCI_ACS_TB);

 	pci_write_config_dword(dev, pos + INTEL_SPT_ACS_CTRL, ctrl);