Re: [PATCH 4/6] PCI/P2PDMA: Remove the DMA_VIRT_OPS hacks

From: Jason Gunthorpe <jgg@ziepe.ca>
To: Christoph Hellwig <hch@lst.de>
Cc: Zhu Yanjun <yanjunz@nvidia.com>,
	Dennis Dalessandro <dennis.dalessandro@cornelisnetworks.com>,
	linux-rdma@vger.kernel.org, linux-pci@vger.kernel.org,
	Mike Marciniszyn <mike.marciniszyn@cornelisnetworks.com>,
	iommu@lists.linux-foundation.org,
	Bjorn Helgaas <bhelgaas@google.com>,
	Bernard Metzler <bmt@zurich.ibm.com>,
	Logan Gunthorpe <logang@deltatee.com>
Subject: Re: [PATCH 4/6] PCI/P2PDMA: Remove the DMA_VIRT_OPS hacks
Date: Thu, 5 Nov 2020 10:34:18 -0400	[thread overview]
Message-ID: <20201105143418.GA4142106@ziepe.ca> (raw)
In-Reply-To: <20201105074205.1690638-5-hch@lst.de>

On Thu, Nov 05, 2020 at 08:42:03AM +0100, Christoph Hellwig wrote:
> Now that all users of dma_virt_ops are gone we can remove the workaround
> for it in the PCI peer to peer code.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: Logan Gunthorpe <logang@deltatee.com>
> Acked-by: Bjorn Helgaas <bhelgaas@google.com>
>  drivers/pci/p2pdma.c | 20 --------------------
>  1 file changed, 20 deletions(-)
> 
> diff --git a/drivers/pci/p2pdma.c b/drivers/pci/p2pdma.c
> index de1c331dbed43f..b07018af53876c 100644
> +++ b/drivers/pci/p2pdma.c
> @@ -556,15 +556,6 @@ int pci_p2pdma_distance_many(struct pci_dev *provider, struct device **clients,
>  		return -1;
>  
>  	for (i = 0; i < num_clients; i++) {
> -#ifdef CONFIG_DMA_VIRT_OPS
> -		if (clients[i]->dma_ops == &dma_virt_ops) {
> -			if (verbose)
> -				dev_warn(clients[i],
> -					 "cannot be used for peer-to-peer DMA because the driver makes use of dma_virt_ops\n");
> -			return -1;
> -		}
> -#endif
> -
>  		pci_client = find_parent_pci_dev(clients[i]);
>  		if (!pci_client) {
>  			if (verbose)
> @@ -837,17 +828,6 @@ static int __pci_p2pdma_map_sg(struct pci_p2pdma_pagemap *p2p_pgmap,
>  	phys_addr_t paddr;
>  	int i;
>  
> -	/*
> -	 * p2pdma mappings are not compatible with devices that use
> -	 * dma_virt_ops. If the upper layers do the right thing
> -	 * this should never happen because it will be prevented
> -	 * by the check in pci_p2pdma_distance_many()
> -	 */
> -#ifdef CONFIG_DMA_VIRT_OPS
> -	if (WARN_ON_ONCE(dev->dma_ops == &dma_virt_ops))
> -		return 0;
> -#endif

The check is removed here, but I didn't see a matching check added to
the IB side? Something like:

static int rdma_rw_map_sg(struct ib_device *dev, struct scatterlist *sg,
			  u32 sg_cnt, enum dma_data_direction dir)
{
	if (is_pci_p2pdma_page(sg_page(sg))) {
		if (ib_uses_virt_dma(dev))
			return 0;
		return pci_p2pdma_map_sg(dev->dma_device, sg, sg_cnt, dir);
	}
	return ib_dma_map_sg(dev, sg, sg_cnt, dir);
}

I think the change to rdma_rw_unmap_sg() should probably be dropped in
favour of the above?

Jason
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