Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751807AbaKGQDR (ORCPT ); Fri, 7 Nov 2014 11:03:17 -0500 Received: from foss-mx-na.foss.arm.com ([217.140.108.86]:54678 "EHLO foss-mx-na.foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750993AbaKGQDQ (ORCPT ); Fri, 7 Nov 2014 11:03:16 -0500 Date: Fri, 7 Nov 2014 16:03:06 +0000 From: Catalin Marinas To: Stefano Stabellini Cc: "xen-devel@lists.xensource.com" , "Ian.Campbell@citrix.com" , "konrad.wilk@oracle.com" , "linux-kernel@vger.kernel.org" , "david.vrabel@citrix.com" , "linux-arm-kernel@lists.infradead.org" Subject: Re: [PATCH v7 6/8] xen/arm/arm64: merge xen/mm32.c into xen/mm.c Message-ID: <20141107160306.GF29148@e104818-lin.cambridge.arm.com> References: <1414422568-19103-6-git-send-email-stefano.stabellini@eu.citrix.com> <20141107142205.GD29148@e104818-lin.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Nov 07, 2014 at 03:28:38PM +0000, Stefano Stabellini wrote: > On Fri, 7 Nov 2014, Catalin Marinas wrote: > > On Mon, Oct 27, 2014 at 03:09:26PM +0000, Stefano Stabellini wrote: > > > Merge xen/mm32.c into xen/mm.c. > > > As a consequence the code gets compiled on arm64 too: introduce a few > > > compat functions to actually be able to compile it. > > > > > > Signed-off-by: Stefano Stabellini > > > Acked-by: Ian Campbell > > > > Since I missed the commit introducing mm32.c (340720be32d4 xen/arm: > > reimplement xen_dma_unmap_page & friends), I'll add a retrospective NAK ;). > > > > The main reason is the asymmetry between dma map and unmap. With host > > swiotlb somehow getting !dma_capable(dev), you even risk leaking dom0 > > swiotlb bounce buffers (on arm64). > > > > > --- a/arch/arm/xen/mm.c > > > +++ b/arch/arm/xen/mm.c > > [...] > > > +/* functions called by SWIOTLB */ > > > + > > > +static void dma_cache_maint(dma_addr_t handle, unsigned long offset, > > > + size_t size, enum dma_data_direction dir, > > > + void (*op)(const void *, size_t, int)) > > > +{ > > > + unsigned long pfn; > > > + size_t left = size; > > > + > > > + pfn = (handle >> PAGE_SHIFT) + offset / PAGE_SIZE; > > > + offset %= PAGE_SIZE; > > > + > > > + do { > > > + size_t len = left; > > > + void *vaddr; > > > + > > > + if (!pfn_valid(pfn)) > > > > Is this the pfn or the mfn? As you said in the previous email, there is > > no mfn_to_pfn() conversion, so that's actually in another address space > > where dom0 pfn_valid() would not make sense. > > That is actually the mfn. The check works because dom0 is mapped 1:1, so > if the mfn is a valid pfn, then it means that it is a local page. So the Xen DMA ops would never be called on anything other than dom0? If that's correct, the pfn_valid() check would work. But add some big comments as it's not clear at all to someone not familiar with Xen. -- Catalin -- 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/