From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:48953) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WsXVd-0001Fn-GZ for qemu-devel@nongnu.org; Thu, 05 Jun 2014 09:15:16 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1WsXVW-00023u-If for qemu-devel@nongnu.org; Thu, 05 Jun 2014 09:15:09 -0400 Message-ID: <53906D54.4030105@suse.de> Date: Thu, 05 Jun 2014 15:15:00 +0200 From: Alexander Graf MIME-Version: 1.0 References: <1401947401-21329-1-git-send-email-aik@ozlabs.ru> <1401947401-21329-2-git-send-email-aik@ozlabs.ru> <5390119D.8040201@ozlabs.ru> <53906B56.3080007@suse.de> <53906C50.50308@ozlabs.ru> In-Reply-To: <53906C50.50308@ozlabs.ru> Content-Type: text/plain; charset=KOI8-R; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH v7 1/4] spapr_iommu: Make in-kernel TCE table optional List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Alexey Kardashevskiy , qemu-devel@nongnu.org Cc: Alex Williamson , qemu-ppc@nongnu.org, Gavin Shan On 05.06.14 15:10, Alexey Kardashevskiy wrote: > On 06/05/2014 11:06 PM, Alexander Graf wrote: >> On 05.06.14 08:43, Alexey Kardashevskiy wrote: >>> On 06/05/2014 03:49 PM, Alexey Kardashevskiy wrote: >>>> POWER KVM supports an KVM_CAP_SPAPR_TCE capability which allows allocating >>>> TCE tables in the host kernel memory and handle H_PUT_TCE requests >>>> targeted to specific LIOBN (logical bus number) right in the host without >>>> switching to QEMU. At the moment this is used for emulated devices only >>>> and the handler only puts TCE to the table. If the in-kernel H_PUT_TCE >>>> handler finds a LIOBN and corresponding table, it will put a TCE to >>>> the table and complete hypercall execution. The user space will not be >>>> notified. >>>> >>>> Upcoming VFIO support is going to use the same sPAPRTCETable device class >>>> so KVM_CAP_SPAPR_TCE is going to be used as well. That means that TCE >>>> tables for VFIO are going to be allocated in the host as well. >>>> However VFIO operates with real IOMMU tables and simple copying of >>>> a TCE to the real hardware TCE table will not work as guest physical >>>> to host physical address translation is requited. >>>> >>>> So until the host kernel gets VFIO support for H_PUT_TCE, we better not >>>> to register VFIO's TCE in the host. >>>> >>>> This adds a bool @kvm_accel flag to the sPAPRTCETable device telling >>>> that sPAPRTCETable should not try allocating TCE table in the host kernel. >>>> Instead, the table will be created in QEMU. >>>> >>>> This adds an kvm_accel parameter to spapr_tce_new_table() to let users >>>> choose whether to use acceleration or not. At the moment it is enabled >>>> for VIO and emulated PCI. Upcoming VFIO support will set it to false. >>>> >>>> Signed-off-by: Alexey Kardashevskiy >>>> --- >>>> >>>> This is a workaround but it lets me have one IOMMU device for VIO, emulated >>>> PCI and VFIO which is a good thing. >>>> >>>> The other way around would be a new KVM_CAP_SPAPR_TCE_VFIO capability but >>>> this needs kernel update. >>> Never mind, I'll make it a capability. I'll post capability reservation >>> patch separately. >> Just rename the flag from "kvm_accel" to "vfio_accel", set it to true for >> vfio and false for emulated devices. Then the spapr_iommu file can check on >> the capability (and default to false for now, since it doesn't exist yet). > Is that ok if the flag does not have to do anything with VFIO per se? :) The flag means "use in-kernel acceleration if the vfio coupling capability is available", no? > > >> That way you don't have to reserve a CAP today. > Why exactly cannot we do that today? Because the CAP namespace isn't a garbage bin we can just throw IDs at. Maybe we realize during patch review that we need completely different CAPs. Alex