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
| ||
|
Date: Wed, 7 Aug 2019 18:56:00 -0700 (PDT) From: Jacob Wen <jian.w.wen@...cle.com> To: Firo Yang <firo.yang@...e.com> Cc: "davem@...emloft.net" <davem@...emloft.net>, "jeffrey.t.kirsher@...el.com" <jeffrey.t.kirsher@...el.com>, "alexander.h.duyck@...ux.intel.com" <alexander.h.duyck@...ux.intel.com>, "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, "netdev@...r.kernel.org" <netdev@...r.kernel.org> Subject: Re: [PATCH v2 1/1] ixgbe: sync the first fragment unconditionally On 8/7/19 4:38 PM, Firo Yang wrote: > The 08/07/2019 15:56, Jacob Wen wrote: >> I think the description is not correct. Consider using something like below. > Thank you for comments. > >> In Xen environment, due to memory fragmentation ixgbe may allocate a 'DMA' >> buffer with pages that are not physically contiguous. > Actually, I didn't look into the reason why ixgbe got a DMA buffer which > was mapped to Xen-swiotlb area. Yes. I was wrong. You don't need to tell the exact reason. > > But I don't think this issue relates to phsical memory contiguity because, in > our case, one ixgbe_rx_buffer only associates at most one page. This is interesting. I guess the performance of the NIC in your environment is not good due to the extra cost of bounce buffer. > > If you take a look at the related code, you will find there are several reasons > for mapping a DMA buffer to Xen-swiotlb area: > static dma_addr_t xen_swiotlb_map_page(struct device *dev, struct page *page, > */ > if (dma_capable(dev, dev_addr, size) && > !range_straddles_page_boundary(phys, size) && > !xen_arch_need_swiotlb(dev, phys, dev_addr) && > swiotlb_force != SWIOTLB_FORCE) > goto done; > > // Firo >> A NIC doesn't support directly write such buffer. So xen-swiotlb would use >> the pages, which are physically contiguous, from the swiotlb buffer for the >> NIC. >> >> The unmap operation is used to copy the swiotlb buffer to the pages that are >> allocated by ixgbe. >> >> On 8/7/19 10:49 AM, Firo Yang wrote: >>> In Xen environment, if Xen-swiotlb is enabled, ixgbe driver >>> could possibly allocate a page, DMA memory buffer, for the first >>> fragment which is not suitable for Xen-swiotlb to do DMA operations. >>> Xen-swiotlb have to internally allocate another page for doing DMA >>> operations. It requires syncing between those two pages. However, >>> since commit f3213d932173 ("ixgbe: Update driver to make use of DMA >>> attributes in Rx path"), the unmap operation is performed with >>> DMA_ATTR_SKIP_CPU_SYNC. As a result, the sync is not performed. >>> >>> To fix this problem, always sync before possibly performing a page >>> unmap operation. >>> >>> Fixes: f3213d932173 ("ixgbe: Update driver to make use of DMA >>> attributes in Rx path") >>> Reviewed-by: Alexander Duyck <alexander.h.duyck@...ux.intel.com> >>> Signed-off-by: Firo Yang <firo.yang@...e.com> >>> --- >>> >>> Changes from v1: >>> * Imporved the patch description. >>> * Added Reviewed-by: and Fixes: as suggested by Alexander Duyck >>> >>> drivers/net/ethernet/intel/ixgbe/ixgbe_main.c | 16 +++++++++------- >>> 1 file changed, 9 insertions(+), 7 deletions(-) >>> >>> diff --git a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c >>> index cbaf712d6529..200de9838096 100644 >>> --- a/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c >>> +++ b/drivers/net/ethernet/intel/ixgbe/ixgbe_main.c >>> @@ -1825,13 +1825,7 @@ static void ixgbe_pull_tail(struct ixgbe_ring *rx_ring, >>> static void ixgbe_dma_sync_frag(struct ixgbe_ring *rx_ring, >>> struct sk_buff *skb) >>> { >>> - /* if the page was released unmap it, else just sync our portion */ >>> - if (unlikely(IXGBE_CB(skb)->page_released)) { >>> - dma_unmap_page_attrs(rx_ring->dev, IXGBE_CB(skb)->dma, >>> - ixgbe_rx_pg_size(rx_ring), >>> - DMA_FROM_DEVICE, >>> - IXGBE_RX_DMA_ATTR); >>> - } else if (ring_uses_build_skb(rx_ring)) { >>> + if (ring_uses_build_skb(rx_ring)) { >>> unsigned long offset = (unsigned long)(skb->data) & ~PAGE_MASK; >>> dma_sync_single_range_for_cpu(rx_ring->dev, >>> @@ -1848,6 +1842,14 @@ static void ixgbe_dma_sync_frag(struct ixgbe_ring *rx_ring, >>> skb_frag_size(frag), >>> DMA_FROM_DEVICE); >>> } >>> + >>> + /* If the page was released, just unmap it. */ >>> + if (unlikely(IXGBE_CB(skb)->page_released)) { >>> + dma_unmap_page_attrs(rx_ring->dev, IXGBE_CB(skb)->dma, >>> + ixgbe_rx_pg_size(rx_ring), >>> + DMA_FROM_DEVICE, >>> + IXGBE_RX_DMA_ATTR); >>> + } >>> } >>> /**
Powered by blists - more mailing lists