[PATCH v7 7/7] iommu/amd: Provide kernel command line option to enable GAPPI

[Sairaj Kodilkar <sarunkod@amd.com>]

Enable GAPPI when the IOMMU GAPPISup extended feature bit is set and
the kernel is booted with the amd_iommu=gappi kernel parameter.

Document the option in Documentation/admin-guide/kernel-parameters.txt
and mechanism in Documentation/arch/x86/iommu.rst.

Co-developed-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Signed-off-by: Sairaj Kodilkar <sarunkod@amd.com>
---
 .../admin-guide/kernel-parameters.txt         |  3 +-
 Documentation/arch/x86/iommu.rst              | 22 +++++++++++++
 drivers/iommu/amd/amd_iommu_types.h           |  2 ++
 drivers/iommu/amd/init.c                      | 33 ++++++++++++++++---
 4 files changed, 55 insertions(+), 5 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 0b3c140babd9..54c01621fc92 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -456,7 +456,8 @@ Kernel parameters
 				          to 4 KiB.
 			v2_pgsizes_only - Limit page-sizes used for v1 page-tables
 				          to 4KiB/2Mib/1GiB.
-
+			gappi           - Use GAPPI instead of GALOG for vCPU
+				          wakeup notification.
 
 	amd_iommu_dump=	[HW,X86-64]
 			Enable AMD IOMMU driver option to dump the ACPI table
diff --git a/Documentation/arch/x86/iommu.rst b/Documentation/arch/x86/iommu.rst
index 79c33560299b..6bac30f5abbd 100644
--- a/Documentation/arch/x86/iommu.rst
+++ b/Documentation/arch/x86/iommu.rst
@@ -150,3 +150,25 @@ AMD Fault reporting
 
 	AMD-Vi: Event logged [IO_PAGE_FAULT domain=0x0007 address=0xffffc02000 flags=0x0000]
 	AMD-Vi: Event logged [IO_PAGE_FAULT device=07:00.0 domain=0x0007 address=0xffffc02000 flags=0x0000]
+
+
+AMD vCPU wakeup Mechanism
+--------------------------
+
+GALOG
+^^^^^
+
+GALOG is a legacy notification path to wakeup the vCPU waiting on an interrupt.
+When IOMMU receives an interrupt destined to vCPU which is scheduled out, it
+updates the vAPIC backing page IRR and appends vCPU tags to a shared GA log
+buffer and raises a single GA log interrupt. IOMMU driver scans this buffer to
+decide which vCPU to wakeup.
+
+GAPPI
+^^^^^
+
+GAPPI is an alternative to GALOG.  With GAPPI enabled, the IOMMU still updates
+the guest vAPIC backing page IRR, but may deliver a physical APIC interrupt
+directly to IRTE[Destination], using IRTE[GATag][7:0] as the vector. This
+distributes host wakeup notifications across CPUs instead of centralizing them
+in a log buffer. This can be enabled by adding option amd_iommu=gappi
diff --git a/drivers/iommu/amd/amd_iommu_types.h b/drivers/iommu/amd/amd_iommu_types.h
index 4600674baf84..47c7e7d28df4 100644
--- a/drivers/iommu/amd/amd_iommu_types.h
+++ b/drivers/iommu/amd/amd_iommu_types.h
@@ -79,6 +79,7 @@
 #define FEATURE_X2APIC		BIT_ULL(2)
 #define FEATURE_NX		BIT_ULL(3)
 #define FEATURE_GT		BIT_ULL(4)
+#define FEATURE_GAPPI		BIT_ULL(5)
 #define FEATURE_IA		BIT_ULL(6)
 #define FEATURE_GA		BIT_ULL(7)
 #define FEATURE_HE		BIT_ULL(8)
@@ -181,6 +182,7 @@
 #define CONTROL_EPH_EN		45
 #define CONTROL_XT_EN		50
 #define CONTROL_INTCAPXT_EN	51
+#define CONTROL_GAPPI_EN	55
 #define CONTROL_GCR3TRPMODE	58
 #define CONTROL_IRTCACHEDIS	59
 #define CONTROL_SNPAVIC_EN	61
diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
index 054ef7262f3c..6a248327047a 100644
--- a/drivers/iommu/amd/init.c
+++ b/drivers/iommu/amd/init.c
@@ -486,6 +486,9 @@ static void iommu_disable(struct amd_iommu *iommu)
 	iommu_feature_disable(iommu, CONTROL_GALOG_EN);
 	iommu_feature_disable(iommu, CONTROL_GAINT_EN);
 
+	/* Disable IOMMU GAPPI */
+	iommu_feature_disable(iommu, CONTROL_GAPPI_EN);
+
 	/* Disable IOMMU PPR logging */
 	iommu_feature_disable(iommu, CONTROL_PPRLOG_EN);
 	iommu_feature_disable(iommu, CONTROL_PPRINT_EN);
@@ -2376,7 +2379,7 @@ static void print_iommu_info(void)
 {
 	int i;
 	static const char * const feat_str[] = {
-		"PreF", "PPR", "X2APIC", "NX", "GT", "[5]",
+		"PreF", "PPR", "X2APIC", "NX", "GT", "GAPPI",
 		"IA", "GA", "HE", "PC"
 	};
 
@@ -3102,6 +3105,13 @@ static void enable_iommus_vapic(void)
 	struct amd_iommu *iommu;
 
 	for_each_iommu(iommu) {
+		/*
+		 * Disable GAPPI, do not check amd_iommu_gappi as it may be
+		 * false in new kexec kernel even though previous kernel has
+		 * enabled it.
+		 */
+		iommu_feature_disable(iommu, CONTROL_GAPPI_EN);
+
 		/*
 		 * Disable GALog if already running. It could have been enabled
 		 * in the previous boot before kdump.
@@ -3131,18 +3141,27 @@ static void enable_iommus_vapic(void)
 	if (!AMD_IOMMU_GUEST_IR_VAPIC(amd_iommu_guest_ir))
 		return;
 
+	if (amd_iommu_gappi &&
+	    !(check_feature(FEATURE_GAPPI) &&
+	      AMD_IOMMU_GUEST_IR_VAPIC(amd_iommu_guest_ir))) {
+		pr_warn("GAPPI is not supported.\n");
+		amd_iommu_gappi = false;
+	}
+
 	/* Enabling GAM and SNPAVIC support */
 	for_each_iommu(iommu) {
-		if (!iommu_ga_log_enable(iommu))
+		if (amd_iommu_gappi)
+			iommu_feature_enable(iommu, CONTROL_GAPPI_EN);
+		else if (!iommu_ga_log_enable(iommu))
 			return;
-
 		iommu_feature_enable(iommu, CONTROL_GAM_EN);
 		if (amd_iommu_snp_en)
 			iommu_feature_enable(iommu, CONTROL_SNPAVIC_EN);
 	}
 
 	amd_iommu_irq_ops.capability |= (1 << IRQ_POSTING_CAP);
-	pr_info("Virtual APIC enabled\n");
+	pr_info("Virtual APIC enabled with %s\n",
+		amd_iommu_gappi ? "GAPPI" : "GALOG");
 #endif
 }
 
@@ -3893,6 +3912,12 @@ static int __init parse_amd_iommu_options(char *str)
 		} else if (strncmp(str, "v2_pgsizes_only", 15) == 0) {
 			pr_info("Restricting V1 page-sizes to 4KiB/2MiB/1GiB");
 			amd_iommu_pgsize_bitmap = AMD_IOMMU_PGSIZES_V2;
+		} else if (strncmp(str, "gappi", 5) == 0) {
+#ifdef CONFIG_IRQ_REMAP
+			amd_iommu_gappi = true;
+#else
+			pr_warn("amd_iommu=gappi ignored, IRQ remapping is not enabled\n");
+#endif
 		} else {
 			pr_notice("Unknown option - '%s'\n", str);
 		}
-- 
2.34.1