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From: Logan Gunthorpe <logang@deltatee.com>
To: linux-kernel@vger.kernel.org, linux-nvme@lists.infradead.org,
	linux-block@vger.kernel.org, linux-pci@vger.kernel.org,
	linux-mm@kvack.org, iommu@lists.linux-foundation.org
Cc: "Stephen Bates" <sbates@raithlin.com>,
	"Christoph Hellwig" <hch@lst.de>,
	"Dan Williams" <dan.j.williams@intel.com>,
	"Jason Gunthorpe" <jgg@ziepe.ca>,
	"Christian König" <christian.koenig@amd.com>,
	"John Hubbard" <jhubbard@nvidia.com>,
	"Don Dutile" <ddutile@redhat.com>,
	"Matthew Wilcox" <willy@infradead.org>,
	"Daniel Vetter" <daniel.vetter@ffwll.ch>,
	"Jakowski Andrzej" <andrzej.jakowski@intel.com>,
	"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>,
	"Logan Gunthorpe" <logang@deltatee.com>
Subject: [PATCH v2 12/22] lib/scatterlist: Add flag for indicating P2PDMA segments in an SGL
Date: Thu, 13 May 2021 16:31:53 -0600	[thread overview]
Message-ID: <20210513223203.5542-13-logang@deltatee.com> (raw)
In-Reply-To: <20210513223203.5542-1-logang@deltatee.com>

Make use of the third free LSB in scatterlist's page_link on 64bit systems.

The extra bit will be used by dma_[un]map_sg_p2pdma() to determine when a
given SGL segments dma_address points to a PCI bus address.
dma_unmap_sg_p2pdma() will need to perform different cleanup when a
segment is marked as P2PDMA.

Using this bit requires adding an additional dependency on CONFIG_64BIT to
CONFIG_PCI_P2PDMA. This should be acceptable as the majority of P2PDMA
use cases are restricted to newer root complexes and roughly require the
extra address space for memory BARs used in the transactions.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
Reviewed-by: John Hubbard <jhubbard@nvidia.com>
---
 drivers/pci/Kconfig         |  2 +-
 include/linux/scatterlist.h | 50 ++++++++++++++++++++++++++++++++++---
 2 files changed, 47 insertions(+), 5 deletions(-)

diff --git a/drivers/pci/Kconfig b/drivers/pci/Kconfig
index 0c473d75e625..90b4bddb3300 100644
--- a/drivers/pci/Kconfig
+++ b/drivers/pci/Kconfig
@@ -163,7 +163,7 @@ config PCI_PASID
 
 config PCI_P2PDMA
 	bool "PCI peer-to-peer transfer support"
-	depends on ZONE_DEVICE
+	depends on ZONE_DEVICE && 64BIT
 	select GENERIC_ALLOCATOR
 	help
 	  Enableѕ drivers to do PCI peer-to-peer transactions to and from
diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h
index 6f70572b2938..562c0aa264f5 100644
--- a/include/linux/scatterlist.h
+++ b/include/linux/scatterlist.h
@@ -58,6 +58,21 @@ struct sg_table {
 #define SG_CHAIN	0x01UL
 #define SG_END		0x02UL
 
+/*
+ * bit 2 is the third free bit in the page_link on 64bit systems which
+ * is used by dma_unmap_sg() to determine if the dma_address is a PCI
+ * bus address when doing P2PDMA.
+ * Note: CONFIG_PCI_P2PDMA depends on CONFIG_64BIT because of this.
+ */
+
+#ifdef CONFIG_PCI_P2PDMA
+#define SG_DMA_PCI_P2PDMA	0x04UL
+#else
+#define SG_DMA_PCI_P2PDMA	0x00UL
+#endif
+
+#define SG_PAGE_LINK_MASK (SG_CHAIN | SG_END | SG_DMA_PCI_P2PDMA)
+
 /*
  * We overload the LSB of the page pointer to indicate whether it's
  * a valid sg entry, or whether it points to the start of a new scatterlist.
@@ -66,7 +81,9 @@ struct sg_table {
 #define sg_is_chain(sg)		((sg)->page_link & SG_CHAIN)
 #define sg_is_last(sg)		((sg)->page_link & SG_END)
 #define sg_chain_ptr(sg)	\
-	((struct scatterlist *) ((sg)->page_link & ~(SG_CHAIN | SG_END)))
+	((struct scatterlist *) ((sg)->page_link & ~SG_PAGE_LINK_MASK))
+
+#define sg_is_dma_pci_p2pdma(sg) ((sg)->page_link & SG_DMA_PCI_P2PDMA)
 
 /**
  * sg_assign_page - Assign a given page to an SG entry
@@ -80,13 +97,13 @@ struct sg_table {
  **/
 static inline void sg_assign_page(struct scatterlist *sg, struct page *page)
 {
-	unsigned long page_link = sg->page_link & (SG_CHAIN | SG_END);
+	unsigned long page_link = sg->page_link & SG_PAGE_LINK_MASK;
 
 	/*
 	 * In order for the low bit stealing approach to work, pages
 	 * must be aligned at a 32-bit boundary as a minimum.
 	 */
-	BUG_ON((unsigned long) page & (SG_CHAIN | SG_END));
+	BUG_ON((unsigned long) page & SG_PAGE_LINK_MASK);
 #ifdef CONFIG_DEBUG_SG
 	BUG_ON(sg_is_chain(sg));
 #endif
@@ -120,7 +137,7 @@ static inline struct page *sg_page(struct scatterlist *sg)
 #ifdef CONFIG_DEBUG_SG
 	BUG_ON(sg_is_chain(sg));
 #endif
-	return (struct page *)((sg)->page_link & ~(SG_CHAIN | SG_END));
+	return (struct page *)((sg)->page_link & ~SG_PAGE_LINK_MASK);
 }
 
 /**
@@ -222,6 +239,31 @@ static inline void sg_unmark_end(struct scatterlist *sg)
 	sg->page_link &= ~SG_END;
 }
 
+/**
+ * sg_dma_mark_pci_p2pdma - Mark the scatterlist entry for PCI p2pdma
+ * @sg:		 SG entryScatterlist
+ *
+ * Description:
+ *   Marks the passed in sg entry to indicate that the dma_address is
+ *   a PCI bus address.
+ **/
+static inline void sg_dma_mark_pci_p2pdma(struct scatterlist *sg)
+{
+	sg->page_link |= SG_DMA_PCI_P2PDMA;
+}
+
+/**
+ * sg_unmark_pci_p2pdma - Unmark the scatterlist entry for PCI p2pdma
+ * @sg:		 SG entryScatterlist
+ *
+ * Description:
+ *   Clears the PCI P2PDMA mark
+ **/
+static inline void sg_dma_unmark_pci_p2pdma(struct scatterlist *sg)
+{
+	sg->page_link &= ~SG_DMA_PCI_P2PDMA;
+}
+
 /**
  * sg_phys - Return physical address of an sg entry
  * @sg:	     SG entry
-- 
2.20.1


  parent reply	other threads:[~2021-05-13 22:32 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-13 22:31 [PATCH v2 00/22] Add new DMA mapping operation for P2PDMA Logan Gunthorpe
2021-05-13 22:31 ` [PATCH v2 01/22] PCI/P2PDMA: Rename upstream_bridge_distance() and rework documentation Logan Gunthorpe
2021-05-13 22:31 ` [PATCH v2 02/22] PCI/P2PDMA: Use a buffer on the stack for collecting the acs list Logan Gunthorpe
2021-05-13 22:31 ` [PATCH v2 03/22] PCI/P2PDMA: Cleanup type for return value of calc_map_type_and_dist() Logan Gunthorpe
2021-05-13 22:31 ` [PATCH v2 04/22] PCI/P2PDMA: Avoid pci_get_slot() which sleeps Logan Gunthorpe
2021-05-13 22:31 ` [PATCH v2 05/22] PCI/P2PDMA: Print a warning if the host bridge is not in the whitelist Logan Gunthorpe
2021-05-13 22:31 ` [PATCH v2 06/22] PCI/P2PDMA: Attempt to set map_type if it has not been set Logan Gunthorpe
2021-05-14 13:49   ` Christoph Hellwig
2021-05-14 16:15     ` Logan Gunthorpe
2021-05-13 22:31 ` [PATCH v2 07/22] PCI/P2PDMA: Refactor pci_p2pdma_map_type() to take pagemap and device Logan Gunthorpe
2021-05-13 22:31 ` [PATCH v2 08/22] dma-mapping: Allow map_sg() ops to return negative error codes Logan Gunthorpe
2021-05-14 13:51   ` Christoph Hellwig
2021-05-14 16:15     ` Logan Gunthorpe
2021-05-13 22:31 ` [PATCH v2 09/22] dma-direct: Return appropriate error code from dma_direct_map_sg() Logan Gunthorpe
2021-05-13 22:31 ` [PATCH v2 10/22] iommu: Return full error code from iommu_map_sg[_atomic]() Logan Gunthorpe
2021-05-13 22:31 ` [PATCH v2 11/22] dma-iommu: Return error code from iommu_dma_map_sg() Logan Gunthorpe
2021-05-13 22:31 ` Logan Gunthorpe [this message]
2021-05-13 22:31 ` [PATCH v2 13/22] PCI/P2PDMA: Make pci_p2pdma_map_type() non-static Logan Gunthorpe
2021-05-13 22:31 ` [PATCH v2 14/22] PCI/P2PDMA: Introduce helpers for dma_map_sg implementations Logan Gunthorpe
2021-05-14 13:53   ` Christoph Hellwig
2021-05-14 16:16     ` Logan Gunthorpe
2021-05-13 22:31 ` [PATCH v2 15/22] dma-direct: Support PCI P2PDMA pages in dma-direct map_sg Logan Gunthorpe
2021-05-14 13:57   ` Christoph Hellwig
2021-05-14 16:17     ` Logan Gunthorpe
2021-05-13 22:31 ` [PATCH v2 16/22] dma-mapping: Add flags to dma_map_ops to indicate PCI P2PDMA support Logan Gunthorpe
2021-05-13 22:31 ` [PATCH v2 17/22] iommu/dma: Support PCI P2PDMA pages in dma-iommu map_sg Logan Gunthorpe
2021-05-13 22:31 ` [PATCH v2 18/22] nvme-pci: Check DMA ops when indicating support for PCI P2PDMA Logan Gunthorpe
2021-05-13 22:32 ` [PATCH v2 19/22] nvme-pci: Convert to using dma_map_sgtable() Logan Gunthorpe
2021-05-13 22:32 ` [PATCH v2 20/22] RDMA/core: Introduce ib_dma_pci_p2p_dma_supported() Logan Gunthorpe
2021-05-13 22:32 ` [PATCH v2 21/22] RDMA/rw: use dma_map_sgtable() Logan Gunthorpe
2021-05-13 22:32 ` [PATCH v2 22/22] PCI/P2PDMA: Remove pci_p2pdma_[un]map_sg() Logan Gunthorpe
2021-05-14 14:00 ` [PATCH v2 00/22] Add new DMA mapping operation for P2PDMA Christoph Hellwig
2021-05-14 16:30   ` Logan Gunthorpe

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