iommu/amd: Introduce Disable IRTE Caching Support

An Interrupt Remapping Table (IRT) stores interrupt remapping configuration
for each device. In a normal operation, the AMD IOMMU caches the table
to optimize subsequent data accesses. This requires the IOMMU driver to
invalidate IRT whenever it updates the table. The invalidation process
includes issuing an INVALIDATE_INTERRUPT_TABLE command following by
a COMPLETION_WAIT command.

However, there are cases in which the IRT is updated at a high rate.
For example, for IOMMU AVIC, the IRTE[IsRun] bit is updated on every
vcpu scheduling (i.e. amd_iommu_update_ga()). On system with large
amount of vcpus and VFIO PCI pass-through devices, the invalidation
process could potentially become a performance bottleneck.

Introducing a new kernel boot option:

    amd_iommu=irtcachedis

which disables IRTE caching by setting the IRTCachedis bit in each IOMMU
Control register, and bypass the IRT invalidation process.

Reviewed-by: Jerry Snitselaar <jsnitsel@redhat.com>
Co-developed-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>
Signed-off-by: Alejandro Jimenez <alejandro.j.jimenez@oracle.com>
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Link: https://lore.kernel.org/r/20230530141137.14376-4-suravee.suthikulpanit@amd.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>

1 files changed, 36 insertions, 0 deletions

diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
index 329a406cc37d..418da641ee3d 100644
--- a/drivers/iommu/amd/init.c
+++ b/drivers/iommu/amd/init.c
@@ -162,6 +162,7 @@ static int amd_iommu_xt_mode = IRQ_REMAP_XAPIC_MODE;
 static bool amd_iommu_detected;
 static bool amd_iommu_disabled __initdata;
 static bool amd_iommu_force_enable __initdata;
+static bool amd_iommu_irtcachedis;
 static int amd_iommu_target_ivhd_type;
 
 /* Global EFR and EFR2 registers */
@@ -484,6 +485,9 @@ static void iommu_disable(struct amd_iommu *iommu)
 
 	/* Disable IOMMU hardware itself */
 	iommu_feature_disable(iommu, CONTROL_IOMMU_EN);
+
+	/* Clear IRTE cache disabling bit */
+	iommu_feature_disable(iommu, CONTROL_IRTCACHEDIS);
 }
 
 /*
@@ -2686,6 +2690,33 @@ static void iommu_enable_ga(struct amd_iommu *iommu)
 #endif
 }
 
+static void iommu_disable_irtcachedis(struct amd_iommu *iommu)
+{
+	iommu_feature_disable(iommu, CONTROL_IRTCACHEDIS);
+}
+
+static void iommu_enable_irtcachedis(struct amd_iommu *iommu)
+{
+	u64 ctrl;
+
+	if (!amd_iommu_irtcachedis)
+		return;
+
+	/*
+	 * Note:
+	 * The support for IRTCacheDis feature is dertermined by
+	 * checking if the bit is writable.
+	 */
+	iommu_feature_enable(iommu, CONTROL_IRTCACHEDIS);
+	ctrl = readq(iommu->mmio_base +  MMIO_CONTROL_OFFSET);
+	ctrl &= (1ULL << CONTROL_IRTCACHEDIS);
+	if (ctrl)
+		iommu->irtcachedis_enabled = true;
+	pr_info("iommu%d (%#06x) : IRT cache is %s\n",
+		iommu->index, iommu->devid,
+		iommu->irtcachedis_enabled ? "disabled" : "enabled");
+}
+
 static void early_enable_iommu(struct amd_iommu *iommu)
 {
 	iommu_disable(iommu);
@@ -2696,6 +2727,7 @@ static void early_enable_iommu(struct amd_iommu *iommu)
 	iommu_set_exclusion_range(iommu);
 	iommu_enable_ga(iommu);
 	iommu_enable_xt(iommu);
+	iommu_enable_irtcachedis(iommu);
 	iommu_enable(iommu);
 	iommu_flush_all_caches(iommu);
 }
@@ -2746,10 +2778,12 @@ static void early_enable_iommus(void)
 		for_each_iommu(iommu) {
 			iommu_disable_command_buffer(iommu);
 			iommu_disable_event_buffer(iommu);
+			iommu_disable_irtcachedis(iommu);
 			iommu_enable_command_buffer(iommu);
 			iommu_enable_event_buffer(iommu);
 			iommu_enable_ga(iommu);
 			iommu_enable_xt(iommu);
+			iommu_enable_irtcachedis(iommu);
 			iommu_set_device_table(iommu);
 			iommu_flush_all_caches(iommu);
 		}
@@ -3402,6 +3436,8 @@ static int __init parse_amd_iommu_options(char *str)
 			amd_iommu_pgtable = AMD_IOMMU_V1;
 		} else if (strncmp(str, "pgtbl_v2", 8) == 0) {
 			amd_iommu_pgtable = AMD_IOMMU_V2;
+		} else if (strncmp(str, "irtcachedis", 11) == 0) {
+			amd_iommu_irtcachedis = true;
 		} else {
 			pr_notice("Unknown option - '%s'\n", str);
 		}