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  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]
Date:	Sat, 20 Feb 2010 12:29:14 -0600
From:	Robert Hancock <hancockrwd@...il.com>
To:	linux-kernel <linux-kernel@...r.kernel.org>,
	netdev <netdev@...r.kernel.org>
Subject: NETIF_F_HIGHDMA misuse in networking drivers?

Was just part of a discussion in another thread talking about 64-bit DMA 
support issues where NETIF_F_HIGHDMA came up. I was originally under the 
impression that this flag indicated the device supported 64-bit DMA 
addressing. However, from looking at the code that checks for it (and, 
well, the actual comment for the flag) it really means "can access 
highmem" which has nothing to do with 64-bit at all. And if there's no 
highmem (like on x86_64) it has no effect at all.

 From looking at some drivers, however, it seems a lot of others had 
similar confusion, as they are doing things like setting NETIF_F_HIGHDMA 
conditionally on whether setting 64-bit DMA mask succeeds:

drivers/net/8139cp.c:

         if (pci_using_dac)
                 dev->features |= NETIF_F_HIGHDMA;

drivers/net/jme.c:

         if (jme->dev->features & NETIF_F_HIGHDMA)
                 rxdesc->desc1.flags = RXFLAG_64BIT;

drivers/net/forcedeth.c:

                 if (dma_64bit) {
                         if (pci_set_dma_mask(pci_dev, DMA_BIT_MASK(39)))
                                 dev_printk(KERN_INFO, &pci_dev->dev,
                                         "64-bit DMA failed, using 
32-bit addressing\n");
                         else
                                 dev->features |= NETIF_F_HIGHDMA;

(the last one is extra funny because it keeps saying 64-bit when it's 
really only 39-bit..)

The net result is that a lot of drivers aren't setting the HIGHDMA flag 
where they should, and thus on architectures where highmem exists, 
resulting in a bunch of unnecessary copying.

Assuming my interpretation is correct, I could try and fix up some of 
this mess.. any comments?
--
To unsubscribe from this list: send the line "unsubscribe netdev" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html

Powered by blists - more mailing lists