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 <a...@ozlabs.ru> >>>>> --- >>>>> >>>>> 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. -- Alexey