linux-kernel - [PATCH v2] iommu/arm-smmu-v3: Match Stall behaviour for S2

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Message-ID: <20240814145633.2565126-1-smostafa@google.com>
Date: Wed, 14 Aug 2024 14:56:33 +0000
From: Mostafa Saleh <smostafa@...gle.com>
To: linux-kernel@...r.kernel.org, iommu@...ts.linux.dev, 
	linux-arm-kernel@...ts.infradead.org, will@...nel.org, robin.murphy@....com, 
	joro@...tes.org
Cc: jean-philippe@...aro.org, jgg@...pe.ca, nicolinc@...dia.com, 
	mshavit@...gle.com, Mostafa Saleh <smostafa@...gle.com>
Subject: [PATCH v2] iommu/arm-smmu-v3: Match Stall behaviour for S2

According to the spec (ARM IHI 0070 F.b), in
"5.5 Fault configuration (A, R, S bits)":
    A STE with stage 2 translation enabled and STE.S2S == 0 is
    considered ILLEGAL if SMMU_IDR0.STALL_MODEL == 0b10.

Also described in the pseudocode “SteIllegal()”
    if eff_idr0_stall_model == '10' && STE.S2S == '0' then
        // stall_model forcing stall, but S2S == 0
        return TRUE;

Which means, S2S must be set when stall model is
"ARM_SMMU_FEAT_STALL_FORCE", but at the moment the driver ignores that.

Although, the driver can do the minimum and only set S2S for
“ARM_SMMU_FEAT_STALL_FORCE”, it is more consistent to match S1
behaviour, which also sets it for “ARM_SMMU_FEAT_STALL” if the
master has requested stalls.

One caveat, is that S2S is not compatible with ATS, this mentioned
in “5.2 Stream Table Entry”:
    In implementations of SMMUv3.1 and later, this configuration is
    ILLEGAL if EATS is not IGNORED and Config[1] == 1 and S2S == 1.

    In SMMUv3.0 implementations, this configuration is ILLEGAL if EATS
    is not IGNORED and S2S == 1

This is also described in the pseudocode “SteIllegal()”

Also, since S2 stalls are enabled now, report them to the IOMMU layer
and for VFIO devices it will fail anyway as VFIO doesn’t register an
iopf handler.

Signed-off-by: Mostafa Saleh <smostafa@...gle.com>

---
v2:
- Fix index of the STE
- Fix conflict with ATS
- Squash the 2 patches and drop enable_nesting
---
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 12 ++++++++----
 drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h |  1 +
 2 files changed, 9 insertions(+), 4 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 a31460f9f3d4..3b70816a2b81 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
@@ -1601,6 +1601,14 @@ void arm_smmu_make_cdtable_ste(struct arm_smmu_ste *target,
 		target->data[2] =
 			cpu_to_le64(FIELD_PREP(STRTAB_STE_2_S2VMID, 0));
 	}
+
+	/*
+	 * S2S is ignored if stage-2 exists but not enabled.
+	 * S2S is not compatible with ATS.
+	 */
+	if (master->stall_enabled && !ats_enabled &&
+	    smmu->features & ARM_SMMU_FEAT_TRANS_S2)
+		target->data[2] |= STRTAB_STE_2_S2S;
 }
 EXPORT_SYMBOL_IF_KUNIT(arm_smmu_make_cdtable_ste);
 
@@ -1739,10 +1747,6 @@ static int arm_smmu_handle_evt(struct arm_smmu_device *smmu, u64 *evt)
 		return -EOPNOTSUPP;
 	}
 
-	/* Stage-2 is always pinned at the moment */
-	if (evt[1] & EVTQ_1_S2)
-		return -EFAULT;
-
 	if (!(evt[1] & EVTQ_1_STALL))
 		return -EOPNOTSUPP;
 
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 14bca41a981b..0dc7ad43c64c 100644
--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.h
@@ -267,6 +267,7 @@ struct arm_smmu_ste {
 #define STRTAB_STE_2_S2AA64		(1UL << 51)
 #define STRTAB_STE_2_S2ENDI		(1UL << 52)
 #define STRTAB_STE_2_S2PTW		(1UL << 54)
+#define STRTAB_STE_2_S2S		(1UL << 57)
 #define STRTAB_STE_2_S2R		(1UL << 58)
 
 #define STRTAB_STE_3_S2TTB_MASK		GENMASK_ULL(51, 4)
-- 
2.46.0.76.ge559c4bf1a-goog