Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754856Ab3JXKdd (ORCPT ); Thu, 24 Oct 2013 06:33:33 -0400 Received: from smtp.citrix.com ([66.165.176.89]:20801 "EHLO SMTP.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754531Ab3JXKdc (ORCPT ); Thu, 24 Oct 2013 06:33:32 -0400 X-IronPort-AV: E=Sophos;i="4.93,561,1378857600"; d="scan'208";a="66880050" Date: Thu, 24 Oct 2013 11:32:26 +0100 From: Stefano Stabellini X-X-Sender: sstabellini@kaball.uk.xensource.com To: Konrad Rzeszutek Wilk CC: Stefano Stabellini , , , , Subject: Re: [PATCH v8 18/19] swiotlb-xen: no need to do execute two bus_to_phys translations in a row In-Reply-To: <20131023195335.GC28963@phenom.dumpdata.com> Message-ID: References: <1382031814-8782-18-git-send-email-stefano.stabellini@eu.citrix.com> <20131023140150.GB27771@phenom.dumpdata.com> <20131023195335.GC28963@phenom.dumpdata.com> User-Agent: Alpine 2.02 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" X-DLP: MIA2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1912 Lines: 46 On Wed, 23 Oct 2013, Konrad Rzeszutek Wilk wrote: > On Wed, Oct 23, 2013 at 06:34:13PM +0100, Stefano Stabellini wrote: > > > 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). > > > > Yeah, I am trying to reduce the number of pfn_to_mfn and mfn_to_pfn > > translations. > > That said, this patch is not needed to have a fully functional > > swiotlb-xen on arm and I would OK with postponing it. > > OK, lets do that as it requires some hard thinking. OK. > > > 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? > > > > No, because on ARM the guest is autotranslate so the pfn returned by > > mfn_to_pfn is always "local". > > However thanks to the m2p_override now we should get the "local" pfn > > from mfn_to_pfn on x86 too. > > I'll test this case though. > > Right, so maybe the pfn_to_mfn_local test is useless nowadays? Yes, I think so. This might be better handled by removing mfn_to_local_pfn altogether. -- 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/