linux-kernel - [RFC PATCH 04/15] lib/scatterlist: Add flag for indicating P2PDMA segments in an SGL

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Date:   Fri,  6 Nov 2020 10:00:25 -0700
From:   Logan Gunthorpe <logang@...tatee.com>
To:     linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org,
        linux-block@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-mm@...ck.org, iommu@...ts.linux-foundation.org
Cc:     Stephen Bates <sbates@...thlin.com>,
        Christoph Hellwig <hch@....de>,
        Dan Williams <dan.j.williams@...el.com>,
        Jason Gunthorpe <jgg@...pe.ca>,
        Christian König <christian.koenig@....com>,
        Ira Weiny <iweiny@...el.com>,
        John Hubbard <jhubbard@...dia.com>,
        Don Dutile <ddutile@...hat.com>,
        Matthew Wilcox <willy@...radead.org>,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        Logan Gunthorpe <logang@...tatee.com>
Subject: [RFC PATCH 04/15] lib/scatterlist: Add flag for indicating P2PDMA segments in an SGL

We make use of the top bit of the dma_length to indicate a P2PDMA
segment. Code that uses this will need to use sg_dma_p2pdma_len() to
get the length and ensure no lengths exceed 2GB.

An sg_dma_is_p2pdma() helper is included to check if a particular
segment is p2pdma().

Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
---
 include/linux/scatterlist.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index 36c47e7e66a2..e738159d56f9 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -39,6 +39,10 @@ struct scatterlist {
 #define sg_dma_len(sg)		((sg)->length)
 #endif
 
+#define SG_P2PDMA_FLAG	(1U << 31)
+#define sg_dma_p2pdma_len(sg)	(sg_dma_len(sg) & ~SG_P2PDMA_FLAG)
+#define sg_dma_is_p2pdma(sg)	(sg_dma_len(sg) & SG_P2PDMA_FLAG)
+
 struct sg_table {
 	struct scatterlist *sgl;	/* the list */
 	unsigned int nents;		/* number of mapped entries */
-- 
2.20.1