Re: [PATCH kernel v3 2/2] powerpc/dma: Fallback to dma_ops when persistent memory present

[Alexey Kardashevskiy]

On 29/10/2020 11:40, Michael Ellerman wrote:
> Alexey Kardashevskiy <aik@xxxxxxxxx> 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