linux-kernel - [PATCH] iommu/arm-smmu-v3: Remove IAS

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Message-ID: <20251211131835.3267022-1-smostafa@google.com>
Date: Thu, 11 Dec 2025 13:18:35 +0000
From: Mostafa Saleh <smostafa@...gle.com>
To: iommu@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org, 
	linux-kernel@...r.kernel.org
Cc: robin.murphy@....com, will@...nel.org, joro@...tes.org, 
	Mostafa Saleh <smostafa@...gle.com>, Tomasz Nowicki <tnowicki@...gle.com>
Subject: [PATCH] iommu/arm-smmu-v3: Remove IAS

The driver only supports AArch64 page tables where OAS == IAS.

Remove the extra IAS tracking for AArch32 as this feature was
never implemented and that was creating BAD_STEs for SMMUv3
with stage-2 and OAS < 40.

Further discussion on this in:
https://lore.kernel.org/linux-iommu/20251130194506.593700-1-smostafa@google.com/

Reported-by: Tomasz Nowicki <tnowicki@...gle.com>
Fixes: f0c453dbcce7 ("iommu/arm-smmu: Ensure IAS is set correctly for AArch32-capable SMMUs")
Signed-off-by: Mostafa Saleh <smostafa@...gle.com>
---
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 18 +++++-------------
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h |  2 --
 2 files changed, 5 insertions(+), 15 deletions(-)

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 d16d35c78c06..019211db621d 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -2551,7 +2551,7 @@ static int arm_smmu_domain_finalise(struct arm_smmu_domain *smmu_domain,
 				     ARM_SMMU_FEAT_VAX) ? 52 : 48;
 
 		pgtbl_cfg.ias = min_t(unsigned long, ias, VA_BITS);
-		pgtbl_cfg.oas = smmu->ias;
+		pgtbl_cfg.oas = smmu->oas;
 		if (enable_dirty)
 			pgtbl_cfg.quirks |= IO_PGTABLE_QUIRK_ARM_HD;
 		fmt = ARM_64_LPAE_S1;
@@ -2561,7 +2561,7 @@ static int arm_smmu_domain_finalise(struct arm_smmu_domain *smmu_domain,
 	case ARM_SMMU_DOMAIN_S2:
 		if (enable_dirty)
 			return -EOPNOTSUPP;
-		pgtbl_cfg.ias = smmu->ias;
+		pgtbl_cfg.ias = smmu->oas;
 		pgtbl_cfg.oas = smmu->oas;
 		fmt = ARM_64_LPAE_S2;
 		finalise_stage_fn = arm_smmu_domain_finalise_s2;
@@ -4395,13 +4395,7 @@ static int arm_smmu_device_hw_probe(struct arm_smmu_device *smmu)
 	}
 
 	/* We only support the AArch64 table format at present */
-	switch (FIELD_GET(IDR0_TTF, reg)) {
-	case IDR0_TTF_AARCH32_64:
-		smmu->ias = 40;
-		fallthrough;
-	case IDR0_TTF_AARCH64:
-		break;
-	default:
+	if (!(FIELD_GET(IDR0_TTF, reg) & IDR0_TTF_AARCH64)) {
 		dev_err(smmu->dev, "AArch64 table format not supported!\n");
 		return -ENXIO;
 	}
@@ -4514,8 +4508,6 @@ static int arm_smmu_device_hw_probe(struct arm_smmu_device *smmu)
 		dev_warn(smmu->dev,
 			 "failed to set DMA mask for table walker\n");
 
-	smmu->ias = max(smmu->ias, smmu->oas);
-
 	if ((smmu->features & ARM_SMMU_FEAT_TRANS_S1) &&
 	    (smmu->features & ARM_SMMU_FEAT_TRANS_S2))
 		smmu->features |= ARM_SMMU_FEAT_NESTING;
@@ -4525,8 +4517,8 @@ static int arm_smmu_device_hw_probe(struct arm_smmu_device *smmu)
 	if (arm_smmu_sva_supported(smmu))
 		smmu->features |= ARM_SMMU_FEAT_SVA;
 
-	dev_info(smmu->dev, "ias %lu-bit, oas %lu-bit (features 0x%08x)\n",
-		 smmu->ias, smmu->oas, smmu->features);
+	dev_info(smmu->dev, "oas %lu-bit (features 0x%08x)\n",
+		 smmu->oas, smmu->features);
 	return 0;
 }
 
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 ae23aacc3840..0a5bb57dbdfe 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
@@ -43,7 +43,6 @@ struct arm_vsmmu;
 #define IDR0_COHACC			(1 << 4)
 #define IDR0_TTF			GENMASK(3, 2)
 #define IDR0_TTF_AARCH64		2
-#define IDR0_TTF_AARCH32_64		3
 #define IDR0_S1P			(1 << 1)
 #define IDR0_S2P			(1 << 0)
 
@@ -784,7 +783,6 @@ struct arm_smmu_device {
 	int				gerr_irq;
 	int				combined_irq;
 
-	unsigned long			ias; /* IPA */
 	unsigned long			oas; /* PA */
 	unsigned long			pgsize_bitmap;
 
-- 
2.52.0.223.gf5cc29aaa4-goog