[PATCH 1/2] iommu/amd: Check feature support bit before accessing MSI capability registers

[Suravee Suthikulpanit]

The IOMMU MMIO access to MSI capability registers is available only if
the EFR[MsiCapMmioSup] is set. Current implementation assumes this bit
is set if the EFR[XtSup] is set, which might not be the case.

Fix by checking the EFR[MsiCapMmioSup] before accessing the MSI address
low/high and MSI data registers via the MMIO.

Fixes: 66929812955b ('iommu/amd: Add support for X2APIC IOMMU interrupts')
Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@xxxxxxx>
---
 drivers/iommu/amd_iommu_init.c  | 17 ++++++++++++-----
 drivers/iommu/amd_iommu_types.h |  1 +
 2 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/drivers/iommu/amd_iommu_init.c b/drivers/iommu/amd_iommu_init.c
index 4413aa6..1dcc0b3 100644
--- a/drivers/iommu/amd_iommu_init.c
+++ b/drivers/iommu/amd_iommu_init.c
@@ -146,7 +146,7 @@ struct ivmd_header {
 bool amd_iommu_irq_remap __read_mostly;
 
 int amd_iommu_guest_ir = AMD_IOMMU_GUEST_IR_VAPIC;
-static int amd_iommu_xt_mode = IRQ_REMAP_X2APIC_MODE;
+static int amd_iommu_xt_mode = IRQ_REMAP_XAPIC_MODE;
 
 static bool amd_iommu_detected;
 static bool __initdata amd_iommu_disabled;
@@ -1531,8 +1531,15 @@ static int __init init_iommu_one(struct amd_iommu *iommu, struct ivhd_header *h)
 			iommu->mmio_phys_end = MMIO_CNTR_CONF_OFFSET;
 		if (((h->efr_reg & (0x1 << IOMMU_EFR_GASUP_SHIFT)) == 0))
 			amd_iommu_guest_ir = AMD_IOMMU_GUEST_IR_LEGACY;
-		if (((h->efr_reg & (0x1 << IOMMU_EFR_XTSUP_SHIFT)) == 0))
-			amd_iommu_xt_mode = IRQ_REMAP_XAPIC_MODE;
+		/*
+		 * Note: Since iommu_update_intcapxt() leverages
+		 * the IOMMU MMIO access to MSI capability block registers
+		 * for MSI address lo/hi/data, we need to check both
+		 * EFR[XtSup] and EFR[MsiCapMmioSup] for x2APIC support.
+		 */
+		if ((h->efr_reg & BIT(IOMMU_EFR_XTSUP_SHIFT)) &&
+		    (h->efr_reg & BIT(IOMMU_EFR_MSICAPMMIOSUP_SHIFT)))
+			amd_iommu_xt_mode = IRQ_REMAP_X2APIC_MODE;
 		break;
 	default:
 		return -EINVAL;
@@ -1981,8 +1988,8 @@ static int iommu_init_intcapxt(struct amd_iommu *iommu)
 	struct irq_affinity_notify *notify = &iommu->intcapxt_notify;
 
 	/**
-	 * IntCapXT requires XTSup=1, which can be inferred
-	 * amd_iommu_xt_mode.
+	 * IntCapXT requires XTSup=1 and MsiCapMmioSup=1,
+	 * which can be inferred from amd_iommu_xt_mode.
 	 */
 	if (amd_iommu_xt_mode != IRQ_REMAP_X2APIC_MODE)
 		return 0;
diff --git a/drivers/iommu/amd_iommu_types.h b/drivers/iommu/amd_iommu_types.h
index 34d63af..89b0c6e 100644
--- a/drivers/iommu/amd_iommu_types.h
+++ b/drivers/iommu/amd_iommu_types.h
@@ -383,6 +383,7 @@
 /* IOMMU Extended Feature Register (EFR) */
 #define IOMMU_EFR_XTSUP_SHIFT	2
 #define IOMMU_EFR_GASUP_SHIFT	7
+#define IOMMU_EFR_MSICAPMMIOSUP_SHIFT	46
 
 #define MAX_DOMAIN_ID 65536
 
-- 
1.8.3.1