From mboxrd@z Thu Jan 1 00:00:00 1970 From: Scott Wood Subject: Re: RFC: vfio API changes needed for powerpc Date: Wed, 3 Apr 2013 14:26:04 -0500 Message-ID: <1365017164.25627.7@snotra> References: <1364943035.24520.28@snotra> <1364960240.2882.230.camel@bling.home> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; delsp=Yes; format=Flowed Content-Transfer-Encoding: 8BIT Cc: Alex Williamson , Wood Scott-B07421 , "kvm@vger.kernel.org" , "agraf@suse.de" , "qemu-devel@nongnu.org" , Yoder Stuart-B08248 , "iommu@lists.linux-foundation.org" , Bhushan Bharat-R65777 To: Stuart Yoder Return-path: Received: from mail-db8lp0187.outbound.messaging.microsoft.com ([213.199.154.187]:29357 "EHLO db8outboundpool.messaging.microsoft.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1763212Ab3DCT0M convert rfc822-to-8bit (ORCPT ); Wed, 3 Apr 2013 15:26:12 -0400 In-Reply-To: (from b08248@gmail.com on Wed Apr 3 14:09:45 2013) Content-Disposition: inline Sender: kvm-owner@vger.kernel.org List-ID: On 04/03/2013 02:09:45 PM, Stuart Yoder wrote: > > Would is be possible for userspace to simply leave room for MSI bank > > mapping (how much room could be determined by something like > > VFIO_IOMMU_GET_MSI_BANK_COUNT) then document the API that userspace > can > > DMA_MAP starting at the 0x0 address of the aperture, growing up, and > > VFIO will map banks on demand at the top of the aperture, growing > down? > > Wouldn't that avoid a lot of issues with userspace needing to know > > anything about MSI banks (other than count) and coordinating irq > numbers > > and enabling handlers? > > This is basically option #A in the original proposals sent. I like > this approach, in that it > is simpler and keeps user space mostly out of this...which is > consistent with how things are done > on x86. User space just needs to know how many windows to leave at > the top of the aperture. > The kernel then has the flexibility to use those windows how it wants. > > But one question, is when should the kernel actually map (and unmap) > the MSI banks. One thing we need to do is enable the aperture...and > current > thinking is that is done on the first DMA_MAP. Similarly when the > last mapping > is unmapped we could also umap the MSI banks. > > Sequence would be something like: > > VFIO_GROUP_SET_CONTAINER // add groups to the container > > VFIO_SET_IOMMU(VFIO_FSL_PAMU) // set iommu model > > cnt = VFIO_IOMMU_GET_MSI_BANK_COUNT // returns max # of > MSI banks > > VFIO_IOMMU_SET_ATTR(ATTR_GEOMETRY) // set overall aperture > > VFIO_IOMMU_SET_ATTR(ATTR_WINDOWS) // set # of windows, > including MSI banks > > VFIO_IOMMU_MAP_DMA // map the guest's memory > ---> kernel enables aperture and maps needed MSI banks > here Maps them where? What if there is more than one explicit DMA mapping? What if DMA mappings are changed during operation? -Scott