From: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
To: stable@vger.kernel.org
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	patches@lists.linux.dev,
	Nicolin Chen <nicolinc@nvidia.com>,
	Will Deacon <will@kernel.org>,
	Sasha Levin <sashal@kernel.org>
Subject: [PATCH 6.12 0923/1102] iommu/tegra241-cmdqv: Publish an LVCMDQ only after it is fully initialized
Date: Thu, 17 Sep 2026 16:14:26 +0100
Message-ID: <20260917151603.806225394@linuxfoundation.org>
In-Reply-To: <20260917151539.408551884@linuxfoundation.org>
References: <20260917151539.408551884@linuxfoundation.org>
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6.12-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Nicolin Chen <nicolinc@nvidia.com>

[ Upstream commit cbc41aacd49e695338940196e7084770365e1b68 ]

tegra241_vintf_init_lvcmdq() stores the freshly allocated vcmdq pointer to
the vintf->lvcmdqs[] array, before tegra241_vcmdq_alloc_smmu_cmdq() builds
the vcmdq->cmdq. The error ISR dereferences that cmdq, so a latched LVCMDQ
error (e.g. one inherited across a kexec) firing in this window would make
tegra241_vintf0_handle_error() pass the still-zeroed arm_smmu_cmdq down to
__arm_smmu_cmdq_skip_err(), dereferencing NULL queue register pointers.

Drop the store from tegra241_vintf_init_lvcmdq() and publish the vcmdq at
the end of the allocation instead, with an smp_store_release() that pairs
with an smp_load_acquire() in the ISR, which can see a fully built LVCMDQ
or NULL.

The user-owned LVCMDQ allocation moves accordingly, publishing the vcmdq
once tegra241_vcmdq_hw_init_user() succeeds, using a plain store since a
user VINTF's lvcmdqs[] has no lockless reader -- the error ISR only walks
the VINTF0 array.

Fixes: 918eb5c856f6 ("iommu/arm-smmu-v3: Add in-kernel support for NVIDIA Tegra241 (Grace) CMDQV")
Assisted-by: Claude:claude-fable-5
Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
Signed-off-by: Will Deacon <will@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 .../iommu/arm/arm-smmu-v3/tegra241-cmdqv.c    | 21 ++++++++++++-------
 1 file changed, 14 insertions(+), 7 deletions(-)

diff --git a/drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.c b/drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.c
index 8d42c63717b6e..2c7b668c84234 100644
--- a/drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.c
+++ b/drivers/iommu/arm/arm-smmu-v3/tegra241-cmdqv.c
@@ -261,12 +261,19 @@ static void tegra241_vintf0_handle_error(struct tegra241_vintf *vintf)
 
 		while (map) {
 			unsigned long lidx = __ffs64(map);
-			struct tegra241_vcmdq *vcmdq = vintf->lvcmdqs[lidx];
-			u32 gerror = readl_relaxed(REG_VCMDQ_PAGE0(vcmdq, GERROR));
+			struct tegra241_vcmdq *vcmdq;
+			u32 gerror;
 
+			map &= ~BIT_ULL(lidx);
+
+			/* Pairs with smp_store_release() publishing it */
+			vcmdq = smp_load_acquire(&vintf->lvcmdqs[lidx]);
+			if (!vcmdq)
+				continue;
+
+			gerror = readl_relaxed(REG_VCMDQ_PAGE0(vcmdq, GERROR));
 			__arm_smmu_cmdq_skip_err(&vintf->cmdqv->smmu, &vcmdq->cmdq);
 			writel(gerror, REG_VCMDQ_PAGE0(vcmdq, GERRORN));
-			map &= ~BIT_ULL(lidx);
 		}
 	}
 }
@@ -541,7 +548,6 @@ static int tegra241_vintf_init_lvcmdq(struct tegra241_vintf *vintf, u16 lidx,
 	vcmdq->page0 = cmdqv->base + TEGRA241_VINTFi_LVCMDQ_PAGE0(idx, lidx);
 	vcmdq->page1 = cmdqv->base + TEGRA241_VINTFi_LVCMDQ_PAGE1(idx, lidx);
 
-	vintf->lvcmdqs[lidx] = vcmdq;
 	return 0;
 }
 
@@ -578,14 +584,15 @@ tegra241_vintf_alloc_lvcmdq(struct tegra241_vintf *vintf, u16 lidx)
 	/* Build an arm_smmu_cmdq for each LVCMDQ */
 	ret = tegra241_vcmdq_alloc_smmu_cmdq(vcmdq);
 	if (ret)
-		goto deinit_lvcmdq;
+		goto free_vcmdq;
+
+	/* Pairs with the smp_load_acquire() in the error ISR */
+	smp_store_release(&vintf->lvcmdqs[lidx], vcmdq);
 
 	dev_dbg(cmdqv->dev,
 		"%sallocated\n", lvcmdq_error_header(vcmdq, header, 64));
 	return vcmdq;
 
-deinit_lvcmdq:
-	tegra241_vintf_deinit_lvcmdq(vintf, lidx);
 free_vcmdq:
 	kfree(vcmdq);
 	return ERR_PTR(ret);
-- 
2.53.0