Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751594AbaKGPgQ (ORCPT ); Fri, 7 Nov 2014 10:36:16 -0500 Received: from smtp02.citrix.com ([66.165.176.63]:49177 "EHLO SMTP02.CITRIX.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751229AbaKGPgO (ORCPT ); Fri, 7 Nov 2014 10:36:14 -0500 X-IronPort-AV: E=Sophos;i="5.07,333,1413244800"; d="scan'208";a="190596674" Date: Fri, 7 Nov 2014 15:28:38 +0000 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" , "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 In-Reply-To: <20141107142205.GD29148@e104818-lin.cambridge.arm.com> Message-ID: References: <1414422568-19103-6-git-send-email-stefano.stabellini@eu.citrix.com> <20141107142205.GD29148@e104818-lin.cambridge.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: MIA2 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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. > Do you use this as a check for foreign pages? If yes, is the mfn for > such pages guaranteed to be different from any valid dom0 pfn? Yes and yes > > + { > > + /* TODO: cache flush */ > > What does this TODO mean here? Which cases are not covered yet? We are going to fill in the cache flush implementation for foreign pages later, in patch 8/8. > > + } else { > > + struct page *page = pfn_to_page(pfn); > > If the pfn here is correct, can you not just have something like: > > void xen_dma_unmap_page(struct device *hwdev, dma_addr_t handle, > size_t size, enum dma_data_direction dir, > struct dma_attrs *attrs) > > { > unsigned long pfn = handle >> PAGE_SHIFT; /* could use some macros */ > if (!pfn_valid(pfn)) { > /* FIXME */ > return; > } > __generic_dma_ops(hwdev)->unmap_page(hwdev, handle, size, dir, attrs); > } Yes, this is possible. Then in patch 8/8 I could remove the FIXME and add a call to a function that issues the new GNTTABOP_cache_flush hypercall. It would also remove the asymmetry you mentioned before because we could do the same for map_page. -- 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/