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SubjectRe: [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);
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