linux-kernel - [RFC] add a struct page* parameter to dma_map_ops.unmap

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-ID: <alpine.DEB.2.02.1411111644490.26318@kaball.uk.xensource.com>
Date:	Mon, 17 Nov 2014 14:11:51 +0000
From:	Stefano Stabellini <stefano.stabellini@...citrix.com>
To:	<gregkh@...uxfoundation.org>
CC:	David Vrabel <david.vrabel@...rix.com>,
	Ian Campbell <Ian.Campbell@...rix.com>,
	<konrad.wilk@...cle.com>, <linux-kernel@...r.kernel.org>,
	<xen-devel@...ts.xensource.com>, <torvalds@...ux-foundation.org>,
	<vinod.koul@...el.com>, <dmaengine@...r.kernel.org>,
	Stefano Stabellini <Stefano.Stabellini@...citrix.com>,
	<bhelgaas@...gle.com>, <jejb@...isc-linux.org>, <deller@....de>,
	<linux-parisc@...r.kernel.org>, <iommu@...ts.linux-foundation.org>,
	<airlied@...ux.ie>, <dri-devel@...ts.freedesktop.org>,
	<alexander.deucher@....com>, <christian.koenig@....com>,
	<linux@....linux.org.uk>, <linux-mips@...ux-mips.org>,
	<ralf@...ux-mips.org>, <linux-arm-kernel@...ts.infradead.org>,
	<dwmw2@...radead.org>
Subject: [RFC] add a struct page* parameter to dma_map_ops.unmap_page

Hi all,
I am writing this email to ask for your advice.

On architectures where dma addresses are different from physical
addresses, it can be difficult to retrieve the physical address of a
page from its dma address.

Specifically this is the case for Xen on arm and arm64 but I think that
other architectures might have the same issue.

Knowing the physical address is necessary to be able to issue any
required cache maintenance operations when unmap_page,
sync_single_for_cpu and sync_single_for_device are called.

Adding a struct page* parameter to unmap_page, sync_single_for_cpu and
sync_single_for_device would make Linux dma handling on Xen on arm and
arm64 much easier and quicker.

I think that other drivers have similar problems, such as the Intel
IOMMU driver having to call find_iova and walking down an rbtree to get
the physical address in its implementation of unmap_page.

Callers have the struct page* in their hands already from the previous
map_page call so it shouldn't be an issue for them.  A problem does
exist however: there are about 280 callers of dma_unmap_page and
pci_unmap_page. We have even more callers of the dma_sync_single_for_*
functions.

Is such a change even conceivable? How would one go about it?

I think that Xen would not be the only one to gain from it, but I would
like to have a confirmation from others: given the magnitude of the
changes involved I would actually prefer to avoid them unless multiple
drivers/archs/subsystems could really benefit from them.

Cheers,

Stefano

diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
index d5d3881..158a765 100644
--- a/include/linux/dma-mapping.h
+++ b/include/linux/dma-mapping.h
@@ -31,8 +31,9 @@ struct dma_map_ops {
 			       unsigned long offset, size_t size,
 			       enum dma_data_direction dir,
 			       struct dma_attrs *attrs);
-	void (*unmap_page)(struct device *dev, dma_addr_t dma_handle,
-			   size_t size, enum dma_data_direction dir,
+	void (*unmap_page)(struct device *dev, struct page *page,
+			   dma_addr_t dma_handle, size_t size,
+			   enum dma_data_direction dir,
 			   struct dma_attrs *attrs);
 	int (*map_sg)(struct device *dev, struct scatterlist *sg,
 		      int nents, enum dma_data_direction dir,
@@ -41,10 +42,10 @@ struct dma_map_ops {
 			 struct scatterlist *sg, int nents,
 			 enum dma_data_direction dir,
 			 struct dma_attrs *attrs);
-	void (*sync_single_for_cpu)(struct device *dev,
+	void (*sync_single_for_cpu)(struct device *dev, struct page *page,
 				    dma_addr_t dma_handle, size_t size,
 				    enum dma_data_direction dir);
-	void (*sync_single_for_device)(struct device *dev,
+	void (*sync_single_for_device)(struct device *dev, struct page *page,
 				       dma_addr_t dma_handle, size_t size,
 				       enum dma_data_direction dir);
 	void (*sync_sg_for_cpu)(struct device *dev,
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/