Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751637Ab3JWODZ (ORCPT ); Wed, 23 Oct 2013 10:03:25 -0400 Received: from aserp1040.oracle.com ([141.146.126.69]:42567 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750936Ab3JWODY (ORCPT ); Wed, 23 Oct 2013 10:03:24 -0400 Date: Wed, 23 Oct 2013 10:01:50 -0400 From: Konrad Rzeszutek Wilk To: Stefano Stabellini Cc: xen-devel@lists.xensource.com, linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, Ian.Campbell@citrix.com Subject: Re: [PATCH v8 18/19] swiotlb-xen: no need to do execute two bus_to_phys translations in a row Message-ID: <20131023140150.GB27771@phenom.dumpdata.com> References: <1382031814-8782-18-git-send-email-stefano.stabellini@eu.citrix.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1382031814-8782-18-git-send-email-stefano.stabellini@eu.citrix.com> User-Agent: Mutt/1.5.21 (2010-09-15) X-Source-IP: acsinet22.oracle.com [141.146.126.238] Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2107 Lines: 56 On Thu, Oct 17, 2013 at 06:43:33PM +0100, Stefano Stabellini wrote: > xen_unmap_single calls xen_bus_to_phys, then passes dev_addr to > is_xen_swiotlb_buffer that calls xen_bus_to_phys again. It does? I see it call mfn_to_local_pfn which calls pfn_to_mfn and get_phys_to_machine (which I presume is going to be a slow operation on ARM). > xen_bus_to_phys is potentially a slow operation that might involve > walking a tree. > We can avoid calling xen_bus_to_phys twice by removing the > is_xen_swiotlb_buffer call and doing the check directly in > xen_unmap_single using the physical address. > > Signed-off-by: Stefano Stabellini Have you tested this with a PFN that is in a foreign domain? I am bit uncomfortable with this - I recall when developing this that I had hit some odd cases of doing DMA of a page to a guest and it not always working. It was the case of not detecting whether the pfn was foreign or not. Sadly I can't recall the details. I would think that this problem would also be present with ARM? But perhaps all the new changes in the pfn_to_mfn that had lately been done have fixed this? > --- > drivers/xen/swiotlb-xen.c | 4 ++-- > 1 files changed, 2 insertions(+), 2 deletions(-) > > diff --git a/drivers/xen/swiotlb-xen.c b/drivers/xen/swiotlb-xen.c > index 4d50058..6d9ca61 100644 > --- a/drivers/xen/swiotlb-xen.c > +++ b/drivers/xen/swiotlb-xen.c > @@ -426,8 +426,8 @@ static void xen_unmap_single(struct device *hwdev, dma_addr_t dev_addr, > > xen_dma_unmap_page(hwdev, paddr, size, dir, attrs); > > - /* NOTE: We use dev_addr here, not paddr! */ > - if (is_xen_swiotlb_buffer(dev_addr)) { > + if (paddr >= virt_to_phys(xen_io_tlb_start) && > + paddr < virt_to_phys(xen_io_tlb_end)) { > swiotlb_tbl_unmap_single(hwdev, paddr, size, dir); > return; > } > -- > 1.7.2.5 > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/