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From: Bart Van Assche <bvanassche@acm.org>
To: Logan Gunthorpe <logang@deltatee.com>,
	linux-kernel@vger.kernel.org, linux-pci@vger.kernel.org,
	linux-nvme@lists.infradead.org, linux-rdma@vger.kernel.org,
	linux-nvdimm@lists.01.org, linux-block@vger.kernel.org
Cc: "Jens Axboe" <axboe@kernel.dk>,
	"Christian König" <christian.koenig@amd.com>,
	"Benjamin Herrenschmidt" <benh@kernel.crashing.org>,
	"Alex Williamson" <alex.williamson@redhat.com>,
	"Jérôme Glisse" <jglisse@redhat.com>,
	"Jason Gunthorpe" <jgg@mellanox.com>,
	"Bjorn Helgaas" <bhelgaas@google.com>,
	"Max Gurtovoy" <maxg@mellanox.com>,
	"Christoph Hellwig" <hch@lst.de>
Subject: Re: [PATCH v7 03/13] PCI/P2PDMA: Add PCI p2pmem DMA mappings to adjust the bus offset
Date: Tue, 25 Sep 2018 10:33:25 -0700	[thread overview]
Message-ID: <1537896805.11137.25.camel@acm.org> (raw)
In-Reply-To: <20180925162231.4354-4-logang@deltatee.com>

On Tue, 2018-09-25 at 10:22 -0600, Logan Gunthorpe wrote:
> +int pci_p2pdma_map_sg(struct device *dev, struct scatterlist *sg, int nents,
> +		      enum dma_data_direction dir)
> +{
> +	struct dev_pagemap *pgmap;
> +	struct scatterlist *s;
> +	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_add_client()
> +	 */
> +	if (WARN_ON_ONCE(IS_ENABLED(CONFIG_DMA_VIRT_OPS) &&
> +			 dev->dma_ops == &dma_virt_ops))
> +		return 0;

Are you assuming that the compiler will optimize out the dev->dma_ops
== &dma_virt_ops test if CONFIG_DMA_VIRT_OPS=n such that no reference to the
dma_virt_ops symbol appears in the object file? Are you sure all compilers
and compiler versions that are used to build the Linux kernel will do that?

Thanks,

Bart.

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  reply	other threads:[~2018-09-25 17:33 UTC|newest]

Thread overview: 25+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-09-25 16:22 [PATCH v7 00/13] Copy Offload in NVMe Fabrics with P2P PCI Memory Logan Gunthorpe
2018-09-25 16:22 ` [PATCH v7 01/13] PCI/P2PDMA: Support peer-to-peer memory Logan Gunthorpe
2018-09-25 17:25   ` Bart Van Assche
2018-09-25 18:09     ` Logan Gunthorpe
2018-09-25 16:22 ` [PATCH v7 02/13] PCI/P2PDMA: Add sysfs group to display p2pmem stats Logan Gunthorpe
2018-09-25 17:29   ` Bart Van Assche
2018-09-25 18:15     ` Logan Gunthorpe
2018-09-25 18:31       ` Bart Van Assche
2018-09-25 18:51         ` Logan Gunthorpe
2018-09-25 16:22 ` [PATCH v7 03/13] PCI/P2PDMA: Add PCI p2pmem DMA mappings to adjust the bus offset Logan Gunthorpe
2018-09-25 17:33   ` Bart Van Assche [this message]
2018-09-25 18:46     ` Logan Gunthorpe
2018-09-25 16:22 ` [PATCH v7 04/13] PCI/P2PDMA: Introduce configfs/sysfs enable attribute helpers Logan Gunthorpe
2018-09-25 16:22 ` [PATCH v7 05/13] docs-rst: Add a new directory for PCI documentation Logan Gunthorpe
2018-09-25 16:22 ` [PATCH v7 06/13] PCI/P2PDMA: Add P2P DMA driver writer's documentation Logan Gunthorpe
2018-09-25 16:22 ` [PATCH v7 07/13] block: Add PCI P2P flag for request queue and check support for requests Logan Gunthorpe
2018-09-25 16:22 ` [PATCH v7 08/13] IB/core: Ensure we map P2P memory correctly in rdma_rw_ctx_[init|destroy]() Logan Gunthorpe
2018-09-25 16:22 ` [PATCH v7 09/13] nvme-pci: Use PCI p2pmem subsystem to manage the CMB Logan Gunthorpe
2018-09-25 16:22 ` [PATCH v7 10/13] nvme-pci: Add support for P2P memory in requests Logan Gunthorpe
2018-09-25 17:11   ` Keith Busch
2018-09-25 17:41     ` Logan Gunthorpe
2018-09-25 17:48       ` Keith Busch
2018-09-25 16:22 ` [PATCH v7 11/13] nvme-pci: Add a quirk for a pseudo CMB Logan Gunthorpe
2018-09-25 16:22 ` [PATCH v7 12/13] nvmet: Introduce helper functions to allocate and free request SGLs Logan Gunthorpe
2018-09-25 16:22 ` [PATCH v7 13/13] nvmet: Optionally use PCI P2P memory Logan Gunthorpe

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