linux-kernel - [PATCH 2/2] iommu/amd: Add support for AVIC when SNP is enabled

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Date:   Tue, 26 Jul 2022 08:43:48 -0500
From:   Suravee Suthikulpanit <suravee.suthikulpanit@....com>
To:     <linux-kernel@...r.kernel.org>, <iommu@...ts.linux.dev>
CC:     <joro@...tes.org>, <will@...nel.org>, <jsnitsel@...hat.com>,
        <vasant.hegde@....com>, <jon.grimm@....com>,
        Suravee Suthikulpanit <suravee.suthikulpanit@....com>
Subject: [PATCH 2/2] iommu/amd: Add support for AVIC when SNP is enabled

In order to support AVIC on SNP-enabled system, The IOMMU driver needs to
check EFR2[SNPAVICSup] and enables the support by setting SNPAVICEn bit
in the IOMMU control register (MMIO offset 18h).

For detail, please see section "SEV-SNP Guest Virtual APIC Support" of the
AMD I/O Virtualization Technology (IOMMU) Specification.
(https://www.amd.com/system/files/TechDocs/48882_IOMMU.pdf)

Signed-off-by: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
---
 drivers/iommu/amd/amd_iommu_types.h |  7 +++++++
 drivers/iommu/amd/init.c            | 11 ++++++++++-
 2 files changed, 17 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/amd/amd_iommu_types.h b/drivers/iommu/amd/amd_iommu_types.h
index 3c1205ba636a..5b1019dab328 100644
--- a/drivers/iommu/amd/amd_iommu_types.h
+++ b/drivers/iommu/amd/amd_iommu_types.h
@@ -103,6 +103,12 @@
 #define FEATURE_GLXVAL_SHIFT	14
 #define FEATURE_GLXVAL_MASK	(0x03ULL << FEATURE_GLXVAL_SHIFT)
 
+/* Extended Feature 2 Bits */
+#define FEATURE_SNPAVICSUP_SHIFT	5
+#define FEATURE_SNPAVICSUP_MASK		(0x07ULL << FEATURE_SNPAVICSUP_SHIFT)
+#define FEATURE_SNPAVICSUP_GAM(x) \
+	((x & FEATURE_SNPAVICSUP_MASK) >> FEATURE_SNPAVICSUP_SHIFT == 0x1)
+
 /* Note:
  * The current driver only support 16-bit PASID.
  * Currently, hardware only implement upto 16-bit PASID
@@ -165,6 +171,7 @@
 #define CONTROL_GAINT_EN	29
 #define CONTROL_XT_EN		50
 #define CONTROL_INTCAPXT_EN	51
+#define CONTROL_SNPAVIC_EN	61
 
 #define CTRL_INV_TO_MASK	(7 << CONTROL_INV_TIMEOUT)
 #define CTRL_INV_TO_NONE	0
diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
index 4cd94d716122..6bbaf6b971e8 100644
--- a/drivers/iommu/amd/init.c
+++ b/drivers/iommu/amd/init.c
@@ -2794,13 +2794,22 @@ static void enable_iommus_vapic(void)
 		return;
 	}
 
-	/* Enabling GAM support */
+	if (amd_iommu_snp_en &&
+	    !FEATURE_SNPAVICSUP_GAM(amd_iommu_efr2)) {
+		pr_warn("Force to disable Virtual APIC due to SNP\n");
+		amd_iommu_guest_ir = AMD_IOMMU_GUEST_IR_LEGACY_GA;
+		return;
+	}
+
+	/* Enabling GAM and SNPAVIC support */
 	for_each_iommu(iommu) {
 		if (iommu_init_ga_log(iommu) ||
 		    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);
-- 
2.34.1