Re: [PATCH 09/16] dma-direct: Support PCI P2PDMA pages in dma-direct map_sg

[Logan Gunthorpe]

On 2021-04-27 1:40 p.m., Jason Gunthorpe wrote:
> On Tue, Apr 27, 2021 at 04:33:51PM -0300, Jason Gunthorpe wrote:
>> On Thu, Apr 08, 2021 at 11:01:16AM -0600, Logan Gunthorpe wrote:
>>> Add PCI P2PDMA support for dma_direct_map_sg() so that it can map
>>> PCI P2PDMA pages directly without a hack in the callers. This allows
>>> for heterogeneous SGLs that contain both P2PDMA and regular pages.
>>>
>>> SGL segments that contain PCI bus addresses are marked with
>>> sg_mark_pci_p2pdma() and are ignored when unmapped.
>>>
>>> Signed-off-by: Logan Gunthorpe <logang@xxxxxxxxxxxx>
>>>  kernel/dma/direct.c | 25 ++++++++++++++++++++++---
>>>  1 file changed, 22 insertions(+), 3 deletions(-)
>>>
>>> diff --git a/kernel/dma/direct.c b/kernel/dma/direct.c
>>> index 002268262c9a..108dfb4ecbd5 100644
>>> +++ b/kernel/dma/direct.c
>>> @@ -13,6 +13,7 @@
>>>  #include <linux/vmalloc.h>
>>>  #include <linux/set_memory.h>
>>>  #include <linux/slab.h>
>>> +#include <linux/pci-p2pdma.h>
>>>  #include "direct.h"
>>>  
>>>  /*
>>> @@ -387,19 +388,37 @@ void dma_direct_unmap_sg(struct device *dev, struct scatterlist *sgl,
>>>  	struct scatterlist *sg;
>>>  	int i;
>>>  
>>> -	for_each_sg(sgl, sg, nents, i)
>>> +	for_each_sg(sgl, sg, nents, i) {
>>> +		if (sg_is_pci_p2pdma(sg)) {
>>> +			sg_unmark_pci_p2pdma(sg);
>>
>> This doesn't seem nice, the DMA layer should only alter the DMA
>> portion of the SG, not the other portions. Is it necessary?
> 
> Oh, I got it completely wrong what this is for.
> 
> This should be named sg_dma_mark_pci_p2p() and similar for other
> functions to make it clear it is part of the DMA side of the SG
> interface (eg it is like sg_dma_address, sg_dma_len, etc)

Fair point. Yes, I'll rename this for the next version.

Logan