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

[Jason Gunthorpe]

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?

Jason