iommu/amd: Indicate whether DMA remap support is enabled

Bit 1 of the IVFS IVInfo field indicates that IOMMU has been used for
pre-boot DMA protection.

Export this capability to allow other places in the kernel to be able to
check for it on AMD systems.

Link: https://www.amd.com/system/files/TechDocs/48882_IOMMU.pdf
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Mario Limonciello <mario.limonciello@amd.com>
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/ce7627fa1c596878ca6515dd9d4381a45b6ee38c.1650878781.git.robin.murphy@arm.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>

drivers/iommu/amd/amd_iommu_types.h

@@ -407,6 +407,7 @@
 /* IOMMU IVINFO */
 #define IOMMU_IVINFO_OFFSET     36
 #define IOMMU_IVINFO_EFRSUP     BIT(0)
+#define IOMMU_IVINFO_DMA_REMAP  BIT(1)
 
 /* IOMMU Feature Reporting Field (for IVHD type 10h */
 #define IOMMU_FEAT_GASUP_SHIFT	6
@@ -449,6 +450,9 @@ extern struct irq_remap_table **irq_lookup_table;
 /* Interrupt remapping feature used? */
 extern bool amd_iommu_irq_remap;
 
+/* IVRS indicates that pre-boot remapping was enabled */
+extern bool amdr_ivrs_remap_support;
+
 /* kmem_cache to get tables with 128 byte alignement */
 extern struct kmem_cache *amd_iommu_irq_cache;
 

drivers/iommu/amd/init.c

@@ -182,6 +182,7 @@ u32 amd_iommu_max_pasid __read_mostly = ~0;
 
 bool amd_iommu_v2_present __read_mostly;
 static bool amd_iommu_pc_present __read_mostly;
+bool amdr_ivrs_remap_support __read_mostly;
 
 bool amd_iommu_force_isolation __read_mostly;
 
@@ -326,6 +327,8 @@ static void __init early_iommu_features_init(struct amd_iommu *iommu,
 {
 	if (amd_iommu_ivinfo & IOMMU_IVINFO_EFRSUP)
 		iommu->features = h->efr_reg;
+	if (amd_iommu_ivinfo & IOMMU_IVINFO_DMA_REMAP)
+		amdr_ivrs_remap_support = true;
 }
 
 /* Access to l1 and l2 indexed register spaces */

drivers/iommu/amd/iommu.c

@@ -2155,6 +2155,8 @@ static bool amd_iommu_capable(enum iommu_cap cap)
 		return (irq_remapping_enabled == 1);
 	case IOMMU_CAP_NOEXEC:
 		return false;
+	case IOMMU_CAP_PRE_BOOT_PROTECTION:
+		return amdr_ivrs_remap_support;
 	default:
 		break;
 	}