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

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Date:   Thu, 29 Oct 2020 11:40:21 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Alexey Kardashevskiy <aik@...abs.ru>, linuxppc-dev@...ts.ozlabs.org
Cc:     Christoph Hellwig <hch@....de>, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org, Alexey Kardashevskiy <aik@...abs.ru>
Subject: Re: [PATCH kernel v3 2/2] powerpc/dma: Fallback to dma_ops when persistent memory present

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);


> @@ -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?

> +	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