From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:59434) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1WsatM-0000Ff-HT for qemu-devel@nongnu.org; Thu, 05 Jun 2014 12:51:59 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1WsatF-0004uf-3h for qemu-devel@nongnu.org; Thu, 05 Jun 2014 12:51:52 -0400 Message-ID: <5390A01D.7020004@suse.de> Date: Thu, 05 Jun 2014 18:51:41 +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> <53907267.1090000@suse.de> <53907FBA.8060604@ozlabs.ru> In-Reply-To: <53907FBA.8060604@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 16:33, Alexey Kardashevskiy wrote: > On 06/05/2014 11:36 PM, Alexander Graf wrote: >> 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? > > No. I need 64bit IOBAs a.k.a. PCI bus addresses. The default DMA window is > just 1 or 2GB and it is mapped at 0 on PCI bus. > > TCEs are 64 bit already. Ok, so the guest has to tell the PCI device to write to a specific window. That's a shame :). > >> What about the missing >> in-kernel modification of the shadow TCEs on H_PUT_TCE? I thought that's >> what this is really about. > This I do not understand :( How does real mode H_PUT_TCE emulation know that it needs to notify user space to establish the map? Alex