linux-kernel - Re: [PATCH v2 0/2] iommu/arm-smmu-v3: make sure the kdump kernel can work well when smmu is enabled

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Date:   Thu, 4 Apr 2019 16:30:31 +0100
From:   Will Deacon <will.deacon@....com>
To:     Zhen Lei <thunder.leizhen@...wei.com>
Cc:     Jean-Philippe Brucker <jean-philippe.brucker@....com>,
        Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        iommu <iommu@...ts.linux-foundation.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 0/2] iommu/arm-smmu-v3: make sure the kdump kernel can
 work well when smmu is enabled

Hi Zhen Lei,

On Mon, Mar 18, 2019 at 09:12:41PM +0800, Zhen Lei wrote:
> v1 --> v2:
> 1. Drop part2. Now, we only use the SMMUv3 hardware feature STE.config=0b000
> (Report abort to device, no event recorded) to suppress the event messages
> caused by the unexpected devices.
> 2. rewrite the patch description.

This issue came up a while back:

https://lore.kernel.org/linux-pci/20180302103032.GB19323@arm.com/

and I'd still prefer to solve it using the disable_bypass logic which we
already have. Something along the lines of the diff below?

We're relying on the DMA API not subsequently requesting a passthrough
domain, but it should only do that if you've configured your crashkernel
to do so.

Will

--->8

diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
index d3880010c6cf..91b8f3b2ee25 100644
--- a/drivers/iommu/arm-smmu-v3.c
+++ b/drivers/iommu/arm-smmu-v3.c
@@ -2454,13 +2454,9 @@ static int arm_smmu_device_reset(struct arm_smmu_device *smmu, bool bypass)
 	/* Clear CR0 and sync (disables SMMU and queue processing) */
 	reg = readl_relaxed(smmu->base + ARM_SMMU_CR0);
 	if (reg & CR0_SMMUEN) {
-		if (is_kdump_kernel()) {
-			arm_smmu_update_gbpa(smmu, GBPA_ABORT, 0);
-			arm_smmu_device_disable(smmu);
-			return -EBUSY;
-		}
-
 		dev_warn(smmu->dev, "SMMU currently enabled! Resetting...\n");
+		WARN_ON(is_kdump_kernel() && !disable_bypass);
+		arm_smmu_update_gbpa(smmu, GBPA_ABORT, 0);
 	}
 
 	ret = arm_smmu_device_disable(smmu);