linux-kernel - [PATCH v7 3/4] iommu/arm: Add BBM Level 2 smmu feature

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Message-ID: <20250617095104.6772-4-miko.lenczewski@arm.com>
Date: Tue, 17 Jun 2025 09:51:03 +0000
From: Mikołaj Lenczewski <miko.lenczewski@....com>
To: ryan.roberts@....com,
	yang@...amperecomputing.com,
	catalin.marinas@....com,
	will@...nel.org,
	jean-philippe@...aro.org,
	robin.murphy@....com,
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	maz@...nel.org,
	oliver.upton@...ux.dev,
	joey.gouly@....com,
	james.morse@....com,
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	jsnitsel@...hat.com,
	mshavit@...gle.com,
	kevin.tian@...el.com,
	linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org,
	iommu@...ts.linux.dev
Cc: Mikołaj Lenczewski <miko.lenczewski@....com>
Subject: [PATCH v7 3/4] iommu/arm: Add BBM Level 2 smmu feature

For supporting BBM Level 2 for userspace mappings, we want to ensure
that the smmu also supports its own version of BBM Level 2. Luckily, the
smmu spec (IHI 0070G 3.21.1.3) is stricter than the aarch64 spec (DDI
0487K.a D8.16.2), so already guarantees that no aborts are raised when
BBM level 2 is claimed.

Add the feature and testing for it under arm_smmu_sva_supported().

Signed-off-by: Mikołaj Lenczewski <miko.lenczewski@....com>
Reviewed-by: Robin Murphy <robin.murphy@....com>
Reviewed-by: Ryan Roberts <ryan.roberts@....com>
---
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c | 3 +++
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c     | 3 +++
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h     | 2 ++
 3 files changed, 8 insertions(+)

diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c
index 0601dece0a0d..59a480974d80 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3-sva.c
@@ -220,6 +220,9 @@ bool arm_smmu_sva_supported(struct arm_smmu_device *smmu)
 		feat_mask |= ARM_SMMU_FEAT_VAX;
 	}
 
+	if (system_supports_bbml2_noabort())
+		feat_mask |= ARM_SMMU_FEAT_BBML2;
+
 	if ((smmu->features & feat_mask) != feat_mask)
 		return false;
 
diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
index 10cc6dc26b7b..39e933086f8f 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -4457,6 +4457,9 @@ static int arm_smmu_device_hw_probe(struct arm_smmu_device *smmu)
 	if (FIELD_GET(IDR3_FWB, reg))
 		smmu->features |= ARM_SMMU_FEAT_S2FWB;
 
+	if (FIELD_GET(IDR3_BBM, reg) == 2)
+		smmu->features |= ARM_SMMU_FEAT_BBML2;
+
 	/* IDR5 */
 	reg = readl_relaxed(smmu->base + ARM_SMMU_IDR5);
 
diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
index ea41d790463e..a33bf520ba97 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
@@ -60,6 +60,7 @@ struct arm_smmu_device;
 #define ARM_SMMU_IDR3			0xc
 #define IDR3_FWB			(1 << 8)
 #define IDR3_RIL			(1 << 10)
+#define IDR3_BBM			GENMASK(12, 11)
 
 #define ARM_SMMU_IDR5			0x14
 #define IDR5_STALL_MAX			GENMASK(31, 16)
@@ -755,6 +756,7 @@ struct arm_smmu_device {
 #define ARM_SMMU_FEAT_HA		(1 << 21)
 #define ARM_SMMU_FEAT_HD		(1 << 22)
 #define ARM_SMMU_FEAT_S2FWB		(1 << 23)
+#define ARM_SMMU_FEAT_BBML2		(1 << 24)
 	u32				features;
 
 #define ARM_SMMU_OPT_SKIP_PREFETCH	(1 << 0)
-- 
2.49.0