Subject: Re: [PATCH 2/5] iommu/arm-smmu-v3: make smmu can be enabled in kdump kernel

From: "Leizhen (ThunderTown)" <[email-masked]>
Date: Fri, 1 Mar 2019 17:18:57 +0800

It seems that the picture is too big, I change it from jpg to png.

On 2019/3/1 17:02, Leizhen (ThunderTown) wrote:
> Hi All,
>     I drew a flowchart, hope this can help you to understand my method.
> 
> On 2019/2/19 15:54, Zhen Lei wrote:
>> To reduce the risk of further crash, the device_shutdown() was not called
>> by the first kernel. That means some devices may still working in the
>> secondary kernel. For example, a netcard may still using ring buffer to
>> receive the broadcast messages in the kdump kernel. No events are reported
>> utill the related smmu reinitialized by the kdump kernel.
>>
>> commit b63b3439b856 ("iommu/arm-smmu-v3: Abort all transactions if SMMU is
>> enabled in kdump kernel") set SMMU_GBPA.ABORT to prevent the unexpected
>> devices accessing, but it also prevent the devices accessing which we
>> needed, like hard disk, netcard.
>>
>> In fact, we can use STE.config=0b000 to abort the unexpected devices
>> accessing only. As below:
>> 1. In the first kernel, all buffers used by the "unexpected" devices are
>>    correctly mapped, and it will not be used by the secondary kernel
>>    because the latter has its dedicated reserved memory.
>> 2. In the secondary kernel, set SMMU_GBPA.ABORT=1 before "disable smmu".
>> 3. In the secondary kernel, after the smmu was disabled, preset all
>>    STE.config=0b000. For 2-level Stream Table, make all L1STD.l2ptr
>>    pointer to a dummy L2ST. The dummy L2ST is shared by all L1STDs.
>> 4. In the secondary kernel, enable smmu. For the needed devices, allocate
>>    new L2STs accordingly.
>>
>> For phase 1 and 2, the unexpected devices base the old mapping access
>> memory, it will not corrupt others. For phase 3, SMMU_GBPA abort it. For
>> phase 4 STE abort it.
>>
>> Fixes: commit b63b3439b856 ("iommu/arm-smmu-v3: Abort all transactions ...")
>> Signed-off-by: Zhen Lei <[email-masked]>
>> ---
>>  drivers/iommu/arm-smmu-v3.c | 72 ++++++++++++++++++++++++++++++++-------------
>>  1 file changed, 51 insertions(+), 21 deletions(-)
>>
>> diff --git a/drivers/iommu/arm-smmu-v3.c b/drivers/iommu/arm-smmu-v3.c
>> index 2072897..c3c4ff2 100644
>> --- a/drivers/iommu/arm-smmu-v3.c
>> +++ b/drivers/iommu/arm-smmu-v3.c
>> @@ -1219,35 +1219,57 @@ static void arm_smmu_init_bypass_stes(u64 *strtab, unsigned int nent)
>>  	}
>>  }
>>
>> -static int arm_smmu_init_l2_strtab(struct arm_smmu_device *smmu, u32 sid)
>> +static int __arm_smmu_init_l2_strtab(struct arm_smmu_device *smmu, u32 sid,
>> +				     struct arm_smmu_strtab_l1_desc *desc)
>>  {
>> -	size_t size;
>>  	void *strtab;
>>  	struct arm_smmu_strtab_cfg *cfg = &smmu->strtab_cfg;
>> -	struct arm_smmu_strtab_l1_desc *desc = &cfg->l1_desc[sid >> STRTAB_SPLIT];
>>
>> -	if (desc->l2ptr)
>> -		return 0;
>> -
>> -	size = 1 << (STRTAB_SPLIT + ilog2(STRTAB_STE_DWORDS) + 3);
>>  	strtab = &cfg->strtab[(sid >> STRTAB_SPLIT) * STRTAB_L1_DESC_DWORDS];
>>
>> -	desc->span = STRTAB_SPLIT + 1;
>> -	desc->l2ptr = dmam_alloc_coherent(smmu->dev, size, &desc->l2ptr_dma,
>> -					  GFP_KERNEL | __GFP_ZERO);
>>  	if (!desc->l2ptr) {
>> -		dev_err(smmu->dev,
>> -			"failed to allocate l2 stream table for SID %u\n",
>> -			sid);
>> -		return -ENOMEM;
>> +		size_t size;
>> +
>> +		size = 1 << (STRTAB_SPLIT + ilog2(STRTAB_STE_DWORDS) + 3);
>> +		desc->l2ptr = dmam_alloc_coherent(smmu->dev, size,
>> +						  &desc->l2ptr_dma,
>> +						  GFP_KERNEL | __GFP_ZERO);
>> +		if (!desc->l2ptr) {
>> +			dev_err(smmu->dev,
>> +				"failed to allocate l2 stream table for SID %u\n",
>> +				sid);
>> +			return -ENOMEM;
>> +		}
>> +
>> +		desc->span = STRTAB_SPLIT + 1;
>> +		arm_smmu_init_bypass_stes(desc->l2ptr, 1 << STRTAB_SPLIT);
>>  	}
>>
>> -	arm_smmu_init_bypass_stes(desc->l2ptr, 1 << STRTAB_SPLIT);
>>  	arm_smmu_write_strtab_l1_desc(strtab, desc);
>> +	return 0;
>> +}
>> +
>> +static int arm_smmu_init_l2_strtab(struct arm_smmu_device *smmu, u32 sid)
>> +{
>> +	int ret;
>> +	struct arm_smmu_strtab_cfg *cfg = &smmu->strtab_cfg;
>> +	struct arm_smmu_strtab_l1_desc *desc = &cfg->l1_desc[sid >> STRTAB_SPLIT];
>> +
>> +	ret = __arm_smmu_init_l2_strtab(smmu, sid, desc);
>> +	if (ret)
>> +		return ret;
>> +
>>  	arm_smmu_sync_std_for_sid(smmu, sid);
>>  	return 0;
>>  }
>>
>> +static int arm_smmu_init_dummy_l2_strtab(struct arm_smmu_device *smmu, u32 sid)
>> +{
>> +	static struct arm_smmu_strtab_l1_desc dummy_desc;
>> +
>> +	return __arm_smmu_init_l2_strtab(smmu, sid, &dummy_desc);
>> +}
>> +
>>  /* IRQ and event handlers */
>>  static irqreturn_t arm_smmu_evtq_thread(int irq, void *dev)
>>  {
>> @@ -2150,8 +2172,12 @@ static int arm_smmu_init_l1_strtab(struct arm_smmu_device *smmu)
>>  	}
>>
>>  	for (i = 0; i < cfg->num_l1_ents; ++i) {
>> -		arm_smmu_write_strtab_l1_desc(strtab, &cfg->l1_desc[i]);
>> -		strtab += STRTAB_L1_DESC_DWORDS << 3;
>> +		if (is_kdump_kernel()) {
>> +			arm_smmu_init_dummy_l2_strtab(smmu, i << STRTAB_SPLIT);
>> +		} else {
>> +			arm_smmu_write_strtab_l1_desc(strtab, &cfg->l1_desc[i]);
>> +			strtab += STRTAB_L1_DESC_DWORDS << 3;
>> +		}
>>  	}
>>
>>  	return 0;
>> @@ -2467,11 +2493,8 @@ 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()) {
>> +		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");
>>  	}
>> @@ -2859,6 +2882,13 @@ static int arm_smmu_device_probe(struct platform_device *pdev)
>>  	struct device *dev = &pdev->dev;
>>  	bool bypass;
>>
>> +	/*
>> +	 * Force to disable bypass for the kdump kernel, abort all incoming
>> +	 * transactions from the unknown devices.
>> +	 */
>> +	if (is_kdump_kernel())
>> +		disable_bypass = 1;
>> +
>>  	smmu = devm_kzalloc(dev, sizeof(*smmu), GFP_KERNEL);
>>  	if (!smmu) {
>>  		dev_err(dev, "failed to allocate arm_smmu_device\n");
>> --
>> 1.8.3
>>
>>
>>
>> .
>>
> 

-- 
Thanks!
BestRegards
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