From: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
To: davem@davemloft.net
Cc: fujita.tomonori@lab.ntt.co.jp, hancockrwd@gmail.com,
linux-kernel@vger.kernel.org, netdev@vger.kernel.org,
linux-usb@vger.kernel.org, bzolnier@gmail.com
Subject: Re: [PATCH RFC] fix problems with NETIF_F_HIGHDMA in networking drivers v2
Date: Wed, 31 Mar 2010 17:35:50 +0900 [thread overview]
Message-ID: <20100331173507I.fujita.tomonori@lab.ntt.co.jp> (raw)
In-Reply-To: <20100325.203520.234306178.davem@davemloft.net>
On Thu, 25 Mar 2010 20:35:20 -0700 (PDT)
David Miller <davem@davemloft.net> wrote:
> From: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
> Date: Fri, 26 Mar 2010 12:33:12 +0900
>
> > On Thu, 25 Mar 2010 19:03:37 -0600
> > Robert Hancock <hancockrwd@gmail.com> wrote:
> >
> >> This seems like it could be a reasonable approach. The only thing is
> >> that in this code you're returning 1 if the parent device has no DMA
> >> mask set. Wouldn't it make more sense to return 0 in this case? I'm
> >> assuming that in that situation it's a virtual device not backed by
> >> any hardware and there should be no DMA mask restriction...
> >
> > I chose the safer option because I don't know enough how net_device
> > structure is used. If returning zero in such case is always safe, it's
> > fine by me. any example of such virtual device driver?
>
> Like Fujita I'd rather play it safe here.
>
> Even for virtual devices, DMA information up to the root bus
> ought to be sane.
Agreed.
Here's the patch in the proper format.
Probably, PCI_DMA_BUS_IS_PHYS should be renamed to something like
DMA_BUS_IS_PHYS and moved to the better place. Then we can avoid
including linux/pci.h.
=
From: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
Subject: [PATCH] net: change illegal_highdma to use dma_mask
Robert Hancock pointed out two problems about NETIF_F_HIGHDMA:
-Many drivers only set the flag when they detect they can use 64-bit DMA,
since otherwise they could receive DMA addresses that they can't handle
(which on platforms without IOMMU/SWIOTLB support is fatal). This means that if
64-bit support isn't available, even buffers located below 4GB will get copied
unnecessarily.
-Some drivers set the flag even though they can't actually handle 64-bit DMA,
which would mean that on platforms without IOMMU/SWIOTLB they would get a DMA
mapping error if the memory they received happened to be located above 4GB.
http://lkml.org/lkml/2010/3/3/530
We can use the dma_mask if we need bouncing or not here. Then we can
safely fix drivers that misuse NETIF_F_HIGHDMA.
Signed-off-by: FUJITA Tomonori <fujita.tomonori@lab.ntt.co.jp>
---
net/core/dev.c | 20 ++++++++++++++------
1 files changed, 14 insertions(+), 6 deletions(-)
diff --git a/net/core/dev.c b/net/core/dev.c
index 5e3dc28..3a09f76 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -129,6 +129,7 @@
#include <linux/jhash.h>
#include <linux/random.h>
#include <trace/events/napi.h>
+#include <linux/pci.h>
#include "net-sysfs.h"
@@ -1790,14 +1791,21 @@ static inline int illegal_highdma(struct net_device *dev, struct sk_buff *skb)
{
#ifdef CONFIG_HIGHMEM
int i;
+ if (!(dev->features & NETIF_F_HIGHDMA)) {
+ for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
+ if (PageHighMem(skb_shinfo(skb)->frags[i].page))
+ return 1;
+ }
- if (dev->features & NETIF_F_HIGHDMA)
- return 0;
-
- for (i = 0; i < skb_shinfo(skb)->nr_frags; i++)
- if (PageHighMem(skb_shinfo(skb)->frags[i].page))
- return 1;
+ if (PCI_DMA_BUS_IS_PHYS) {
+ struct device *pdev = dev->dev.parent;
+ for (i = 0; i < skb_shinfo(skb)->nr_frags; i++) {
+ dma_addr_t addr = page_to_phys(skb_shinfo(skb)->frags[i].page);
+ if (!pdev->dma_mask || addr + PAGE_SIZE - 1 > *pdev->dma_mask)
+ return 1;
+ }
+ }
#endif
return 0;
}
--
1.7.0
next prev parent reply other threads:[~2010-03-31 8:36 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-03-04 2:55 [PATCH RFC] fix problems with NETIF_F_HIGHDMA in networking drivers v2 Robert Hancock
2010-03-04 4:58 ` FUJITA Tomonori
2010-03-26 1:03 ` Robert Hancock
2010-03-26 3:33 ` FUJITA Tomonori
2010-03-26 3:35 ` David Miller
2010-03-31 8:35 ` FUJITA Tomonori [this message]
2010-04-02 2:53 ` David Miller
2010-03-10 20:17 ` Roland Dreier
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