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

From: "Leizhen (ThunderTown)" <[email-masked]>
Date: Wed, 17 Apr 2019 09:39:30 +0800

On 2019/4/16 17:14, Will Deacon wrote:
> On Mon, Apr 08, 2019 at 10:31:47AM +0800, Leizhen (ThunderTown) wrote:
>> On 2019/4/4 23:30, Will Deacon wrote:
>>> 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/[email-masked]/
>>>
>>> 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?
>>
>> Yes, my patches also use disable_bypass=1(set ste.config=0b000). If
>> SMMU_IDR0.ST_LEVEL=0(Linear Stream table supported), then all STE entries
>> are allocated and initialized(set ste.config=0b000). But if SMMU_IDR0.ST_LEVEL=1
>> (2-level Stream Table), we only allocated and initialized the first level tables,
>> but leave level 2 tables dynamic allocated. That means, C_BAD_STREAMID(eventid=0x2)
>> will be reported, if an unexpeted device access memory without reinitialized in
>> kdump kernel.
> 
> So is your problem just that the C_BAD_STREAMID events are noisy? If so,
> perhaps we should be disabling fault reporting entirely in the kdump kernel.
> 
> How about the update diff below? I'm keen to have this as simple as
> possible, so we don't end up introducing rarely tested, complex code on
> the crash path.
In theory, it can solve the problem, let me test it.

But then again, below patch will also disable the fault reporting come from the
expected devices which are used in the kdump kernel. In fact, my patches have been
merged into our interval version more than 2 months, no bug have been found yet.

However, my patches do not support the case that the hardware does not support the
"STE bypass" feature, I think your patch can also resolve it.

> 
> Will
> 
> --->8
> 
> diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
> index d3880010c6cf..d8b73da6447d 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);
> @@ -2553,6 +2549,8 @@ static int arm_smmu_device_reset(struct arm_smmu_device *smmu, bool bypass)
>  		return ret;
>  	}
>  
> +	if (is_kdump_kernel())
> +		enables &= ~(CR0_EVTQEN | CR0_PRIQEN);
>  
>  	/* Enable the SMMU interface, or ensure bypass */
>  	if (!bypass || disable_bypass) {
> 
> .
> 

-- 
Thanks!
BestRegards

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