From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:59320) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WsXqc-0000X0-9A for qemu-devel@nongnu.org; Thu, 05 Jun 2014 09:36:58 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1WsXqT-0003wB-S5 for qemu-devel@nongnu.org; Thu, 05 Jun 2014 09:36:50 -0400 Message-ID: <53907267.1090000@suse.de> Date: Thu, 05 Jun 2014 15:36:39 +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> <53906D54.4030105@suse.de> <5390718C.4020005@ozlabs.ru> In-Reply-To: <5390718C.4020005@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 15:33, Alexey Kardashevskiy wrote: > On 06/05/2014 11:15 PM, Alexander Graf wrote: >> 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? > It is a flag of sPAPRTCETable which is not supposed to know about VFIO at > all, it is just an IOMMU. But if you are ok with it, I have no reason to be > unhappy either :) > > > >>>> 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. > That was my first plan - to wait for KVM_CAP_SPAPR_TCE_64 be available in > the kernel. So all you need are 64bit TCEs with bus_offset? What about the missing in-kernel modification of the shadow TCEs on H_PUT_TCE? I thought that's what this is really about. Alex