Re: [PATCH v9 5/8] block: set FOLL_PCI_P2PDMA in __bio_iov_iter_get_pages()

From: John Hubbard <jhubbard@nvidia.com>
To: Logan Gunthorpe <logang@deltatee.com>,
	linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org,
	linux-block@vger.kernel.org, linux-pci@vger.kernel.org,
	linux-mm@kvack.org
Cc: "Christoph Hellwig" <hch@lst.de>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>,
	"Dan Williams" <dan.j.williams@intel.com>,
	"Jason Gunthorpe" <jgg@ziepe.ca>,
	"Christian König" <christian.koenig@amd.com>,
	"Don Dutile" <ddutile@redhat.com>,
	"Matthew Wilcox" <willy@infradead.org>,
	"Daniel Vetter" <daniel.vetter@ffwll.ch>,
	"Minturn Dave B" <dave.b.minturn@intel.com>,
	"Jason Ekstrand" <jason@jlekstrand.net>,
	"Dave Hansen" <dave.hansen@linux.intel.com>,
	"Xiong Jianxin" <jianxin.xiong@intel.com>,
	"Bjorn Helgaas" <helgaas@kernel.org>,
	"Ira Weiny" <ira.weiny@intel.com>,
	"Robin Murphy" <robin.murphy@arm.com>,
	"Martin Oliveira" <martin.oliveira@eideticom.com>,
	"Chaitanya Kulkarni" <ckulkarnilinux@gmail.com>,
	"Ralph Campbell" <rcampbell@nvidia.com>,
	"Stephen Bates" <sbates@raithlin.com>
Subject: Re: [PATCH v9 5/8] block: set FOLL_PCI_P2PDMA in __bio_iov_iter_get_pages()
Date: Mon, 5 Sep 2022 17:48:05 -0700	[thread overview]
Message-ID: <21eda152-c2ec-26bb-92f9-507b5378cd99@nvidia.com> (raw)
In-Reply-To: <20220825152425.6296-6-logang@deltatee.com>

On 8/25/22 08:24, Logan Gunthorpe wrote:
> When a bio's queue supports PCI P2PDMA, set FOLL_PCI_P2PDMA for
> iov_iter_get_pages_flags(). This allows PCI P2PDMA pages to be passed
> from userspace and enables the O_DIRECT path in iomap based filesystems
> and direct to block devices.

Oh great, more O_DIRECT code paths. :)

> 
> Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
> ---
>  block/bio.c | 10 ++++++++--
>  1 file changed, 8 insertions(+), 2 deletions(-)
> 
> diff --git a/block/bio.c b/block/bio.c
> index 969607bc1f4d..ca09d79a0683 100644
> --- a/block/bio.c
> +++ b/block/bio.c
> @@ -1200,6 +1200,7 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
>  	unsigned short entries_left = bio->bi_max_vecs - bio->bi_vcnt;
>  	struct bio_vec *bv = bio->bi_io_vec + bio->bi_vcnt;
>  	struct page **pages = (struct page **)bv;
> +	unsigned int flags = 0;

It would be nice to name this gup_flags, instead.

>  	ssize_t size, left;
>  	unsigned len, i = 0;
>  	size_t offset, trim;
> @@ -1213,6 +1214,10 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
>  	BUILD_BUG_ON(PAGE_PTRS_PER_BVEC < 2);
>  	pages += entries_left * (PAGE_PTRS_PER_BVEC - 1);
>  
> +	if (bio->bi_bdev && bio->bi_bdev->bd_disk &&
> +	    blk_queue_pci_p2pdma(bio->bi_bdev->bd_disk->queue))
> +		flags |= FOLL_PCI_P2PDMA;
> +
>  	/*
>  	 * Each segment in the iov is required to be a block size multiple.
>  	 * However, we may not be able to get the entire segment if it spans
> @@ -1220,8 +1225,9 @@ static int __bio_iov_iter_get_pages(struct bio *bio, struct iov_iter *iter)
>  	 * result to ensure the bio's total size is correct. The remainder of
>  	 * the iov data will be picked up in the next bio iteration.
>  	 */
> -	size = iov_iter_get_pages2(iter, pages, UINT_MAX - bio->bi_iter.bi_size,
> -				  nr_pages, &offset);
> +	size = iov_iter_get_pages_flags(iter, pages,
> +					UINT_MAX - bio->bi_iter.bi_size,
> +					nr_pages, &offset, flags);
>  	if (unlikely(size <= 0))
>  		return size ? size : -EFAULT;
>  

Looks good. After applying Christoph's tweak, and optionally the gup_flags
rename as well, please feel free to add:

Reviewed-by: John Hubbard <jhubbard@nvidia.com>

thanks,

-- 
John Hubbard
NVIDIA