On Thu, 25 Mar 2010 20:35:20 -0700 (PDT) David Miller <davem@xxxxxxxxxxxxx> wrote: > From: FUJITA Tomonori <fujita.tomonori@xxxxxxxxxxxxx> > Date: Fri, 26 Mar 2010 12:33:12 +0900 > > > On Thu, 25 Mar 2010 19:03:37 -0600 > > Robert Hancock <hancockrwd@xxxxxxxxx> 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@xxxxxxxxxxxxx> 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@xxxxxxxxxxxxx> --- 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 -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
