From mboxrd@z Thu Jan 1 00:00:00 1970 From: David Vrabel Subject: Re: [Xen-devel] [PATCH 1/1] XEN: Use correct masking in xen_swiotlb_alloc_coherent. Date: Fri, 31 Aug 2012 13:47:05 +0100 Message-ID: <5040B249.4000306@citrix.com> References: <1346407072-6405-1-git-send-email-stefano.panella@citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1346407072-6405-1-git-send-email-stefano.panella@citrix.com> Sender: linux-kernel-owner@vger.kernel.org To: Stefano Panella Cc: linux-kernel@vger.kernel.org, konrad.wilk@oracle.com, xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org 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... 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) > phys = virt_to_phys(ret); > dev_addr = xen_phys_to_bus(phys); David