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From: Vidya Sagar <vidyas@nvidia.com>
To: <corbet@lwn.net>, <bhelgaas@google.com>, <galshalom@nvidia.com>,
	<leonro@nvidia.com>, <jgg@nvidia.com>, <treding@nvidia.com>,
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	<linux-kernel@vger.kernel.org>, <kthota@nvidia.com>,
	<mmaddireddy@nvidia.com>, <vidyas@nvidia.com>, <sagar.tv@gmail.com>
Subject: [PATCH V3] PCI: Extend ACS configurability
Date: Thu, 23 May 2024 12:05:28 +0530
Message-ID: <20240523063528.199908-1-vidyas@nvidia.com>
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For iommu_groups to form correctly, the ACS settings in the PCIe fabric
need to be setup early in the boot process, either via the BIOS or via
the kernel disable_acs_redir parameter.

disable_acs_redir allows clearing the RR|CR|EC ACS flags, but the PCIe
spec Rev3.0 already defines 7 different ACS related flags with many more
useful combinations depending on the fabric design.

For backward compatibility, leave the 'disable_acs_redir' as is and add
a new parameter 'config_acs'so that the user can directly specify the ACS
flags to set on a per-device basis. Use a similar syntax to the existing
'resource_alignment'  parameter by using the @ character and have the user
specify the ACS flags using a bit encoding. If both 'disable_acs_redir' and
'config_acs' are specified for a particular device, configuration specified
through 'config_acs' takes precedence over the other.

Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
---
v3:
* Fixed a documentation issue reported by kernel test bot

v2:
* Refactored the code as per Jason's suggestion

 .../admin-guide/kernel-parameters.txt         |  22 +++
 drivers/pci/pci.c                             | 148 +++++++++++-------
 2 files changed, 112 insertions(+), 58 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 41644336e..b4a8207eb 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4456,6 +4456,28 @@
 				bridges without forcing it upstream. Note:
 				this removes isolation between devices and
 				may put more devices in an IOMMU group.
+		config_acs=
+				Format:
+				=<ACS flags>@<pci_dev>[; ...]
+				Specify one or more PCI devices (in the format
+				specified above) optionally prepended with flags
+				and separated by semicolons. The respective
+				capabilities will be enabled, disabled or unchanged
+				based on what is specified in flags.
+				ACS Flags is defined as follows
+				bit-0 : ACS Source Validation
+				bit-1 : ACS Translation Blocking
+				bit-2 : ACS P2P Request Redirect
+				bit-3 : ACS P2P Completion Redirect
+				bit-4 : ACS Upstream Forwarding
+				bit-5 : ACS P2P Egress Control
+				bit-6 : ACS Direct Translated P2P
+				Each bit can be marked as
+				‘0‘ – force disabled
+				‘1’ – force enabled
+				‘x’ – unchanged.
+				Note: this may remove isolation between devices
+				and may put more devices in an IOMMU group.
 		force_floating	[S390] Force usage of floating interrupts.
 		nomio		[S390] Do not use MIO instructions.
 		norid		[S390] ignore the RID field and force use of
diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
index a607f277c..a46264f83 100644
--- a/drivers/pci/pci.c
+++ b/drivers/pci/pci.c
@@ -887,30 +887,67 @@ void pci_request_acs(void)
 }
 
 static const char *disable_acs_redir_param;
+static const char *config_acs_param;
 
-/**
- * pci_disable_acs_redir - disable ACS redirect capabilities
- * @dev: the PCI device
- *
- * For only devices specified in the disable_acs_redir parameter.
- */
-static void pci_disable_acs_redir(struct pci_dev *dev)
+struct pci_acs {
+	u16 cap;
+	u16 ctrl;
+	u16 fw_ctrl;
+};
+
+static void __pci_config_acs(struct pci_dev *dev, struct pci_acs *caps,
+			     const char *p, u16 mask, u16 flags)
 {
+	char *delimit;
 	int ret = 0;
-	const char *p;
-	int pos;
-	u16 ctrl;
 
-	if (!disable_acs_redir_param)
+	if (!p)
 		return;
 
-	p = disable_acs_redir_param;
 	while (*p) {
+		if (!mask) {
+			/* Check for ACS flags */
+			delimit = strstr(p, "@");
+			if (delimit) {
+				int end;
+				u32 shift = 0;
+
+				end = delimit - p - 1;
+
+				while (end > -1) {
+					if (*(p + end) == '0') {
+						mask |= 1 << shift;
+						shift++;
+						end--;
+					} else if (*(p + end) == '1') {
+						mask |= 1 << shift;
+						flags |= 1 << shift;
+						shift++;
+						end--;
+					} else if ((*(p + end) == 'x') || (*(p + end) == 'X')) {
+						shift++;
+						end--;
+					} else {
+						pci_err(dev, "Invalid ACS flags... Ignoring\n");
+						return;
+					}
+				}
+				p = delimit + 1;
+			} else {
+				pci_err(dev, "ACS Flags missing\n");
+				return;
+			}
+		}
+
+		if (mask & ~(PCI_ACS_SV | PCI_ACS_TB | PCI_ACS_RR | PCI_ACS_CR |
+			    PCI_ACS_UF | PCI_ACS_EC | PCI_ACS_DT)) {
+			pci_err(dev, "Invalid ACS flags specified\n");
+			return;
+		}
+
 		ret = pci_dev_str_match(dev, p, &p);
 		if (ret < 0) {
-			pr_info_once("PCI: Can't parse disable_acs_redir parameter: %s\n",
-				     disable_acs_redir_param);
-
+			pr_info_once("PCI: Can't parse acs command line parameter\n");
 			break;
 		} else if (ret == 1) {
 			/* Found a match */
@@ -930,56 +967,38 @@ static void pci_disable_acs_redir(struct pci_dev *dev)
 	if (!pci_dev_specific_disable_acs_redir(dev))
 		return;
 
-	pos = dev->acs_cap;
-	if (!pos) {
-		pci_warn(dev, "cannot disable ACS redirect for this hardware as it does not have ACS capabilities\n");
-		return;
-	}
-
-	pci_read_config_word(dev, pos + PCI_ACS_CTRL, &ctrl);
+	pci_dbg(dev, "ACS mask  = 0x%X\n", mask);
+	pci_dbg(dev, "ACS flags = 0x%X\n", flags);
 
-	/* P2P Request & Completion Redirect */
-	ctrl &= ~(PCI_ACS_RR | PCI_ACS_CR | PCI_ACS_EC);
+	/* If mask is 0 then we copy the bit from the firmware setting. */
+	caps->ctrl = (caps->ctrl & ~mask) | (caps->fw_ctrl & mask);
+	caps->ctrl |= flags;
 
-	pci_write_config_word(dev, pos + PCI_ACS_CTRL, ctrl);
-
-	pci_info(dev, "disabled ACS redirect\n");
+	pci_info(dev, "Configured ACS to 0x%x\n", caps->ctrl);
 }
 
 /**
  * pci_std_enable_acs - enable ACS on devices using standard ACS capabilities
  * @dev: the PCI device
+ * @caps: default ACS controls
  */
-static void pci_std_enable_acs(struct pci_dev *dev)
+static void pci_std_enable_acs(struct pci_dev *dev, struct pci_acs *caps)
 {
-	int pos;
-	u16 cap;
-	u16 ctrl;
-
-	pos = dev->acs_cap;
-	if (!pos)
-		return;
-
-	pci_read_config_word(dev, pos + PCI_ACS_CAP, &cap);
-	pci_read_config_word(dev, pos + PCI_ACS_CTRL, &ctrl);
-
 	/* Source Validation */
-	ctrl |= (cap & PCI_ACS_SV);
+	caps->ctrl |= (caps->cap & PCI_ACS_SV);
 
 	/* P2P Request Redirect */
-	ctrl |= (cap & PCI_ACS_RR);
+	caps->ctrl |= (caps->cap & PCI_ACS_RR);
 
 	/* P2P Completion Redirect */
-	ctrl |= (cap & PCI_ACS_CR);
+	caps->ctrl |= (caps->cap & PCI_ACS_CR);
 
 	/* Upstream Forwarding */
-	ctrl |= (cap & PCI_ACS_UF);
+	caps->ctrl |= (caps->cap & PCI_ACS_UF);
 
 	/* 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);
+		caps->ctrl |= (caps->cap & PCI_ACS_TB);
 }
 
 /**
@@ -988,23 +1007,33 @@ static void pci_std_enable_acs(struct pci_dev *dev)
  */
 static void pci_enable_acs(struct pci_dev *dev)
 {
-	if (!pci_acs_enable)
-		goto disable_acs_redir;
+	struct pci_acs caps;
+	int pos;
+
+	pos = dev->acs_cap;
+	if (!pos)
+		return;
 
-	if (!pci_dev_specific_enable_acs(dev))
-		goto disable_acs_redir;
+	pci_read_config_word(dev, pos + PCI_ACS_CAP, &caps.cap);
+	pci_read_config_word(dev, pos + PCI_ACS_CTRL, &caps.ctrl);
+	caps.fw_ctrl = caps.ctrl;
 
-	pci_std_enable_acs(dev);
+	/* If an iommu is present we start with kernel default caps */
+	if (pci_acs_enable) {
+		if (pci_dev_specific_enable_acs(dev))
+			pci_std_enable_acs(dev, &caps);
+	}
 
-disable_acs_redir:
 	/*
-	 * Note: pci_disable_acs_redir() must be called even if ACS was not
-	 * enabled by the kernel because it may have been enabled by
-	 * platform firmware.  So if we are told to disable it, we should
-	 * always disable it after setting the kernel's default
-	 * preferences.
+	 * Always apply caps from the command line, even if there is no iommu.
+	 * Trust that the admin has a reason to change the ACS settings.
 	 */
-	pci_disable_acs_redir(dev);
+	__pci_config_acs(dev, &caps, disable_acs_redir_param,
+			 PCI_ACS_RR | PCI_ACS_CR | PCI_ACS_EC,
+			 ~(PCI_ACS_RR | PCI_ACS_CR | PCI_ACS_EC));
+	__pci_config_acs(dev, &caps, config_acs_param, 0, 0);
+
+	pci_write_config_word(dev, pos + PCI_ACS_CTRL, caps.ctrl);
 }
 
 /**
@@ -7023,6 +7052,8 @@ 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 (!strncmp(str, "config_acs=", 11)) {
+				config_acs_param = str + 11;
 			} else {
 				pr_err("PCI: Unknown option `%s'\n", str);
 			}
@@ -7047,6 +7078,7 @@ static int __init pci_realloc_setup_params(void)
 	resource_alignment_param = kstrdup(resource_alignment_param,
 					   GFP_KERNEL);
 	disable_acs_redir_param = kstrdup(disable_acs_redir_param, GFP_KERNEL);
+	config_acs_param = kstrdup(config_acs_param, GFP_KERNEL);
 
 	return 0;
 }
-- 
2.25.1