linux-kernel - Re: [PATCH kernel v3 2/2] powerpc/dma: Fallback to dma

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Message-ID: <2f285412-9e19-7888-1102-f50658c43b9d@ozlabs.ru>
Date:   Thu, 29 Oct 2020 11:46:59 +1100
From:   Alexey Kardashevskiy <aik@...abs.ru>
To:     Michael Ellerman <mpe@...erman.id.au>,
        linuxppc-dev@...ts.ozlabs.org
Cc:     Christoph Hellwig <hch@....de>, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH kernel v3 2/2] powerpc/dma: Fallback to dma_ops when
 persistent memory present



On 29/10/2020 11:40, Michael Ellerman wrote:
> Alexey Kardashevskiy <aik@...abs.ru> writes:
>> diff --git a/arch/powerpc/platforms/pseries/iommu.c b/arch/powerpc/platforms/pseries/iommu.c
>> index e4198700ed1a..91112e748491 100644
>> --- a/arch/powerpc/platforms/pseries/iommu.c
>> +++ b/arch/powerpc/platforms/pseries/iommu.c
>> @@ -1111,11 +1112,13 @@ static void reset_dma_window(struct pci_dev *dev, struct device_node *par_dn)
>>    */
>>   static u64 enable_ddw(struct pci_dev *dev, struct device_node *pdn)
>>   {
>> -	int len, ret;
>> +	int len = 0, ret;
>> +	bool pmem_present = of_find_node_by_type(NULL, "ibm,pmemory") != NULL;
> 
> That leaks a reference on the returned node.
> 
> 	dn = of_find_node_by_type(NULL, "ibm,pmemory");
> 	pmem_present = dn != NULL;
> 	of_node_put(dn);


ah, true. v4 then.


> 
> 
>> @@ -1126,7 +1129,7 @@ static u64 enable_ddw(struct pci_dev *dev, struct device_node *pdn)
>>   
>>   	mutex_lock(&direct_window_init_mutex);
>>   
>> -	dma_addr = find_existing_ddw(pdn);
>> +	dma_addr = find_existing_ddw(pdn, &len);
> 
> I don't see len used anywhere?
> 
>>   	if (dma_addr != 0)
>>   		goto out_unlock;
>>   
>> @@ -1212,14 +1215,26 @@ static u64 enable_ddw(struct pci_dev *dev, struct device_node *pdn)
>>   	}
>>   	/* verify the window * number of ptes will map the partition */
>>   	/* check largest block * page size > max memory hotplug addr */
>> -	max_addr = ddw_memory_hotplug_max();
>> -	if (query.largest_available_block < (max_addr >> page_shift)) {
>> -		dev_dbg(&dev->dev, "can't map partition max 0x%llx with %llu "
>> -			  "%llu-sized pages\n", max_addr,  query.largest_available_block,
>> -			  1ULL << page_shift);
>> +	/*
>> +	 * The "ibm,pmemory" can appear anywhere in the address space.
>> +	 * Assuming it is still backed by page structs, try MAX_PHYSMEM_BITS
>> +	 * for the upper limit and fallback to max RAM otherwise but this
>> +	 * disables device::dma_ops_bypass.
>> +	 */
>> +	len = max_ram_len;
> 
> Here you override whatever find_existing_ddw() wrote to len?


Not always, there is a bunch of gotos before this line to the end of the 
function and one (which returns the existing window) is legit. Thanks,



> 
>> +	if (pmem_present) {
>> +		if (query.largest_available_block >=
>> +		    (1ULL << (MAX_PHYSMEM_BITS - page_shift)))
>> +			len = MAX_PHYSMEM_BITS - page_shift;
>> +		else
>> +			dev_info(&dev->dev, "Skipping ibm,pmemory");
>> +	}
>> +
>> +	if (query.largest_available_block < (1ULL << (len - page_shift))) {
>> +		dev_dbg(&dev->dev, "can't map partition max 0x%llx with %llu %llu-sized pages\n",
>> +			1ULL << len, query.largest_available_block, 1ULL << page_shift);
>>   		goto out_failed;
>>   	}
>> -	len = order_base_2(max_addr);
>>   	win64 = kzalloc(sizeof(struct property), GFP_KERNEL);
>>   	if (!win64) {
>>   		dev_info(&dev->dev,
> 
> 
> cheers
> 

-- 
Alexey