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Mon, 03 Feb 2020 13:00:54 -0500 X-MC-Unique: 3ZDtis_GPGyUQxhELM89nA-1 Received: from smtp.corp.redhat.com (int-mx05.intmail.prod.int.phx2.redhat.com [10.5.11.15]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id 47A3C13E6; Mon, 3 Feb 2020 18:00:52 +0000 (UTC) Received: from w520.home (ovpn-116-28.phx2.redhat.com [10.3.116.28]) by smtp.corp.redhat.com (Postfix) with ESMTP id 5108B8642F; Mon, 3 Feb 2020 18:00:46 +0000 (UTC) Date: Mon, 3 Feb 2020 11:00:45 -0700 From: Alex Williamson To: "Liu, Yi L" Subject: Re: [RFC v3 4/8] vfio/type1: Add VFIO_NESTING_GET_IOMMU_UAPI_VERSION Message-ID: <20200203110045.1fb3ec8d@w520.home> In-Reply-To: References: <1580299912-86084-1-git-send-email-yi.l.liu@intel.com> <1580299912-86084-5-git-send-email-yi.l.liu@intel.com> <20200129165649.43008300@w520.home> MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.15 Cc: "Tian, Kevin" , "Raj, Ashok" , "kvm@vger.kernel.org" , "jean-philippe.brucker@arm.com" , "Tian, Jun J" , "iommu@lists.linux-foundation.org" , "linux-kernel@vger.kernel.org" , "Sun, Yi Y" X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On Fri, 31 Jan 2020 13:04:11 +0000 "Liu, Yi L" wrote: > Hi Alex, > > > From: Alex Williamson [mailto:alex.williamson@redhat.com] > > Sent: Thursday, January 30, 2020 7:57 AM > > To: Liu, Yi L > > Subject: Re: [RFC v3 4/8] vfio/type1: Add > > VFIO_NESTING_GET_IOMMU_UAPI_VERSION > > > > On Wed, 29 Jan 2020 04:11:48 -0800 > > "Liu, Yi L" wrote: > > > > > From: Liu Yi L > > > > > > In Linux Kernel, the IOMMU nesting translation (a.k.a. IOMMU dual stage > > > translation capability) is abstracted in uapi/iommu.h, in which the uAPIs > > > like bind_gpasid/iommu_cache_invalidate/fault_report/pgreq_resp are defined. > > > > > > VFIO_TYPE1_NESTING_IOMMU stands for the vfio iommu type which is backed by > > > IOMMU nesting translation capability. VFIO exposes the nesting capability > > > to userspace and also exposes uAPIs (will be added in later patches) to user > > > space for setting up nesting translation from userspace. Thus applications > > > like QEMU could support vIOMMU for pass-through devices with IOMMU nesting > > > translation capability. > > > > > > As VFIO expose the nesting IOMMU programming to userspace, it also needs to > > > provide an API for the uapi/iommu.h version check to ensure compatibility. > > > This patch reports the iommu uapi version to userspace. Applications could > > > use this API to do version check before further using the nesting uAPIs. > > > > > > Cc: Kevin Tian > > > CC: Jacob Pan > > > Cc: Alex Williamson > > > Cc: Eric Auger > > > Cc: Jean-Philippe Brucker > > > Signed-off-by: Liu Yi L > > > --- > > > drivers/vfio/vfio.c | 3 +++ > > > include/uapi/linux/vfio.h | 10 ++++++++++ > > > 2 files changed, 13 insertions(+) > > > > > > diff --git a/drivers/vfio/vfio.c b/drivers/vfio/vfio.c > > > index 425d60a..9087ad4 100644 > > > --- a/drivers/vfio/vfio.c > > > +++ b/drivers/vfio/vfio.c > > > @@ -1170,6 +1170,9 @@ static long vfio_fops_unl_ioctl(struct file *filep, > > > case VFIO_GET_API_VERSION: > > > ret = VFIO_API_VERSION; > > > break; > > > + case VFIO_NESTING_GET_IOMMU_UAPI_VERSION: > > > + ret = iommu_get_uapi_version(); > > > + break; > > > > Shouldn't the type1 backend report this? It doesn't make much sense > > that the spapr backend reports a version for something it doesn't > > support. Better yet, provide this info gratuitously in the > > VFIO_IOMMU_GET_INFO ioctl return like you do with nesting in the next > > patch, then it can help the user figure out if this support is present. > > yeah, it would be better to report it by type1 backed. However, > it is kind of issue when QEMU using it. > > My series "hooks" vSVA supports on VFIO_TYPE1_NESTING_IOMMU type. > [RFC v3 09/25] vfio: check VFIO_TYPE1_NESTING_IOMMU support > https://www.spinics.net/lists/kvm/msg205197.html > > In QEMU, it will determine the iommu type firstly and then invoke > VFIO_SET_IOMMU. I think before selecting VFIO_TYPE1_NESTING_IOMMU, > QEMU needs to check the IOMMU uAPI version. If IOMMU uAPI is incompatible, > QEMU should not use VFIO_TYPE1_NESTING_IOMMU type. If > VFIO_NESTING_GET_IOMMU_UAPI_VERSION is available after set iommu, then it > may be an issue. That's why this series reports the version in vfio layer > instead of type1 backend. Why wouldn't you use CHECK_EXTENSION? You could probe specifically for a VFIO_TYP1_NESTING_IOMMU_UAPI_VERSION extension that returns the version number. Thanks, Alex _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu