From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757321Ab2IDOsG (ORCPT ); Tue, 4 Sep 2012 10:48:06 -0400 Received: from rcsinet15.oracle.com ([148.87.113.117]:30244 "EHLO rcsinet15.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757175Ab2IDOsE (ORCPT ); Tue, 4 Sep 2012 10:48:04 -0400 Date: Tue, 4 Sep 2012 10:37:31 -0400 From: Konrad Rzeszutek Wilk To: Stefano Panella Cc: David Vrabel , "linux-kernel@vger.kernel.org" , "xen-devel@lists.xensource.com" Subject: Re: [Xen-devel] [PATCH 1/1] XEN: Use correct masking in xen_swiotlb_alloc_coherent. Message-ID: <20120904143731.GC23361@phenom.dumpdata.com> References: <1346407072-6405-1-git-send-email-stefano.panella@citrix.com> <5040B249.4000306@citrix.com> <20120831164010.GA18929@localhost.localdomain> <50460B2E.3020200@citrix.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <50460B2E.3020200@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 On Tue, Sep 04, 2012 at 03:07:42PM +0100, Stefano Panella wrote: > On 08/31/2012 05:40 PM, Konrad Rzeszutek Wilk wrote: > >On Fri, Aug 31, 2012 at 01:47:05PM +0100, David Vrabel wrote: > >>On 31/08/12 10:57, Stefano Panella wrote: > >>>When running 32-bit pvops-dom0 and a driver tries to allocate a coherent > >>>DMA-memory the xen swiotlb-implementation returned memory beyond 4GB. > >>> > >>>This caused for example not working sound on a system with 4 GB and a 64-bit > >>>compatible sound-card with sets the DMA-mask to 64bit. > >>> > >>>On bare-metal and the forward-ported xen-dom0 patches from OpenSuse a coherent > >>>DMA-memory is always allocated inside the 32-bit address-range by calling > >>>dma_alloc_coherent_mask. > >>We should have the same behaviour under Xen as bare metal so: > >> > >>Acked-By: David Vrabel > >> > >>This does limit the DMA mask to 32-bits by passing it through an > >>unsigned long, which seems a bit sneaky... > >so is the issue that we are not casting it from 'u64' to 'u32' > >(unsigned long) on 32-bit? > > Yes. I do not completely understand why but I think on 32-bit kernel we need to cast dma_mask to u32. This is done automatically using dma_alloc_coherent_mask() > > > > >>Presumably the sound card is capable of handling 64 bit physical > >>addresses (or it would break under 64-bit kernels) so it's not clear why > >>this sound driver requires this restriction. > >> > >>Is there a bug in the sound driver or sound subsystem where it's > >>truncating a dma_addr_t by assigning it to an unsigned long or similar? > >> > >>>--- a/drivers/xen/swiotlb-xen.c > >>>+++ b/drivers/xen/swiotlb-xen.c > >>>@@ -232,7 +232,7 @@ xen_swiotlb_alloc_coherent(struct device *hwdev, size_t size, > >>> return ret; > >>> if (hwdev && hwdev->coherent_dma_mask) > >>>- dma_mask = hwdev->coherent_dma_mask; > >>>+ dma_mask = dma_alloc_coherent_mask(hwdev, flags); > >>Suggest > >> > >> if (hwdev) > >> dma_mask = dma_alloc_coherent_mask(hwdev, flags) > > I can change the patch like that if you like. > > >Isn't that code just doing this: > >atic inline unsigned long dma_alloc_coherent_mask(struct device *dev, > > gfp_t gfp) > >{ > > unsigned long dma_mask = 0; > > > > dma_mask = dev->coherent_dma_mask; > > if (!dma_mask) > > dma_mask = (gfp & GFP_DMA) ? DMA_BIT_MASK(24) : > >DMA_BIT_MASK(32); > > > > return dma_mask; > >} > > > >and in our code, the dma_mask by default is DMA_BIT_MASK(32): > > > >u64 dma_mask = DMA_BIT_MASK(32); > > > >So what I am missing? > > I am not sure what you mean with "what am I missing?" > > Current code looks like: > > void * > xen_swiotlb_alloc_coherent(struct device *hwdev, size_t size, > dma_addr_t *dma_handle, gfp_t flags, > struct dma_attrs *attrs) > { > void *ret; > int order = get_order(size); > u64 dma_mask = DMA_BIT_MASK(32); > unsigned long vstart; > phys_addr_t phys; > dma_addr_t dev_addr; > > /* > * Ignore region specifiers - the kernel's ideas of > * pseudo-phys memory layout has nothing to do with the > * machine physical layout. We can't allocate highmem > * because we can't return a pointer to it. > */ > flags &= ~(__GFP_DMA | __GFP_HIGHMEM); > > if (dma_alloc_from_coherent(hwdev, size, dma_handle, &ret)) > return ret; > > vstart = __get_free_pages(flags, order); > ret = (void *)vstart; > > if (!ret) > return ret; > > if (hwdev && hwdev->coherent_dma_mask) > dma_mask = hwdev->coherent_dma_mask; > > > So if hwdev->coherent_dma_mask is set to 0xffffffffffffffff our dma_mask will > be u64 set to 0xffffffffffffffff even if we set it to DMA_BIT_MASK(32) previously. That is what I was missing. Let me include that in the git commit and also put this patch on the stable tree. > > I hope I am not getting this wrong and let me know if I should send an updated version > of the patch including David V. change. > > Regards, > > Stefano