Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758943Ab3IFQKO (ORCPT ); Fri, 6 Sep 2013 12:10:14 -0400 Received: from smtp02.citrix.com ([66.165.176.63]:36304 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756548Ab3IFQKL (ORCPT ); Fri, 6 Sep 2013 12:10:11 -0400 X-IronPort-AV: E=Sophos;i="4.90,855,1371081600"; d="scan'208";a="48953948" Date: Fri, 6 Sep 2013 17:09:52 +0100 From: Stefano Stabellini X-X-Sender: sstabellini@kaball.uk.xensource.com To: Catalin Marinas CC: Stefano Stabellini , "xen-devel@lists.xensource.com" , "Ian.Campbell@citrix.com" , "linux-kernel@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "konrad.wilk@oracle.com" Subject: Re: [PATCH v5 11/13] xen: introduce xen_alloc/free_coherent_pages In-Reply-To: <20130906155928.GH1946@arm.com> Message-ID: References: <1377801154-29215-11-git-send-email-stefano.stabellini@eu.citrix.com> <20130905160905.GI11887@arm.com> <20130906141444.GE1946@arm.com> <20130906155928.GH1946@arm.com> User-Agent: Alpine 2.02 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" X-DLP: MIA1 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2306 Lines: 51 On Fri, 6 Sep 2013, Catalin Marinas wrote: > On Fri, Sep 06, 2013 at 03:59:02PM +0100, Stefano Stabellini wrote: > > On Fri, 6 Sep 2013, Catalin Marinas wrote: > > > On Thu, Sep 05, 2013 at 05:43:33PM +0100, Stefano Stabellini wrote: > > > > On Thu, 5 Sep 2013, Catalin Marinas wrote: > > > > > On Thu, Aug 29, 2013 at 07:32:32PM +0100, Stefano Stabellini wrote: > > > > > > xen_swiotlb_alloc_coherent needs to allocate a coherent buffer for cpu > > > > > > and devices. On native x86 and ARMv8 is sufficient to call > > > > > > __get_free_pages in order to get a coherent buffer, while on ARM we need > > > > > > to call arm_dma_ops.alloc. > > > > > > > > > > Don't bet on this for ARMv8. It's not mandated for the architecture, so > > > > > at some point some SoC will require non-cacheable buffers for coherency. > > > > > > > > I see. > > > > Would it be better if I implemented xen_alloc_coherent_pages on armv8 by > > > > calling arm64_swiotlb_dma_ops.alloc? > > > > > > What does this buffer do exactly? Is it allocated by guests? > > > > It is allocated by Dom0 to do DMA to/from a device. > > It is the buffer that is going to be returned by dma_map_ops.alloc to > > the caller: > > > > On x86: > > dma_map_ops.alloc -> xen_swiotlb_alloc_coherent -> xen_alloc_coherent_pages -> __get_free_pages > > > > On ARM: > > dma_map_ops.alloc -> xen_swiotlb_alloc_coherent -> xen_alloc_coherent_pages -> arm_dma_ops.alloc > > > > On ARM64 > > dma_map_ops.alloc -> xen_swiotlb_alloc_coherent -> xen_alloc_coherent_pages -> ???? > > OK, I'm getting more confused. Do all the above calls happen in the > guest, Dom0, or a mix? I guess the confusion comes from a difference in terminology: dom0 is a guest like the others, just a bit more privileged. We usually call domU a normal unprivileged guest. The above calls would happen in Dom0 (when an SMMU is not available). They could also happen in a DomU if we assign a physical device to it (and an SMMU is not available). So in general they would happen in any guest that needs to program a real device. -- 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/