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Message-ID: <51BEE965.5040509@suse.de> Date: Mon, 17 Jun 2013 12:48:05 +0200 From: Alexander Graf <agraf@...e.de> To: Alexey Kardashevskiy <aik@...abs.ru> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>, linuxppc-dev@...ts.ozlabs.org, David Gibson <david@...son.dropbear.id.au>, Paul Mackerras <paulus@...ba.org>, kvm@...r.kernel.org, linux-kernel@...r.kernel.org, kvm-ppc@...r.kernel.org Subject: Re: [PATCH 1/4] KVM: PPC: Add support for multiple-TCE hcalls On 06/17/2013 12:46 PM, Alexander Graf wrote: > On 06/17/2013 10:51 AM, Alexey Kardashevskiy wrote: >> On 06/17/2013 06:40 PM, Alexander Graf wrote: >>> On 17.06.2013, at 10:34, Alexey Kardashevskiy wrote: >>> >>>> On 06/17/2013 06:02 PM, Alexander Graf wrote: >>>>> On 17.06.2013, at 09:55, Alexey Kardashevskiy wrote: >>>>> >>>>>> On 06/17/2013 08:06 AM, Alexander Graf wrote: >>>>>>> On 05.06.2013, at 08:11, Alexey Kardashevskiy wrote: >>>>>>> >>>>>>>> This adds real mode handlers for the H_PUT_TCE_INDIRECT and >>>>>>>> H_STUFF_TCE hypercalls for QEMU emulated devices such as >>>>>>>> IBMVIO devices or emulated PCI. These calls allow adding >>>>>>>> multiple entries (up to 512) into the TCE table in one call >>>>>>>> which saves time on transition to/from real mode. >>>>>>>> >>>>>>>> This adds a tce_tmp cache to kvm_vcpu_arch to save valid TCEs >>>>>>>> (copied from user and verified) before writing the whole list >>>>>>>> into the TCE table. This cache will be utilized more in the >>>>>>>> upcoming VFIO/IOMMU support to continue TCE list processing in >>>>>>>> the virtual mode in the case if the real mode handler failed >>>>>>>> for some reason. >>>>>>>> >>>>>>>> This adds a guest physical to host real address converter and >>>>>>>> calls the existing H_PUT_TCE handler. The converting function >>>>>>>> is going to be fully utilized by upcoming VFIO supporting >>>>>>>> patches. >>>>>>>> >>>>>>>> This also implements the KVM_CAP_PPC_MULTITCE capability, so >>>>>>>> in order to support the functionality of this patch, QEMU >>>>>>>> needs to query for this capability and set the >>>>>>>> "hcall-multi-tce" hypertas property only if the capability is >>>>>>>> present, otherwise there will be serious performance >>>>>>>> degradation. >>>>>>>> >>>>>>>> Cc: David Gibson<david@...son.dropbear.id.au> Signed-off-by: >>>>>>>> Alexey Kardashevskiy<aik@...abs.ru> Signed-off-by: Paul >>>>>>>> Mackerras<paulus@...ba.org> >>>>>>> Only a few minor nits. Ben already commented on implementation >>>>>>> details. >>>>>>> >>>>>>>> --- Changelog: 2013/06/05: * fixed mistype about IBMVIO in the >>>>>>>> commit message * updated doc and moved it to another section * >>>>>>>> changed capability number >>>>>>>> >>>>>>>> 2013/05/21: * added kvm_vcpu_arch::tce_tmp * removed cleanup >>>>>>>> if put_indirect failed, instead we do not even start writing >>>>>>>> to TCE table if we cannot get TCEs from the user and they are >>>>>>>> invalid * kvmppc_emulated_h_put_tce is split to >>>>>>>> kvmppc_emulated_put_tce and kvmppc_emulated_validate_tce (for >>>>>>>> the previous item) * fixed bug with failthrough for H_IPI * >>>>>>>> removed all get_user() from real mode handlers * >>>>>>>> kvmppc_lookup_pte() added (instead of making lookup_linux_pte >>>>>>>> public) --- Documentation/virtual/kvm/api.txt | 17 ++ >>>>>>>> arch/powerpc/include/asm/kvm_host.h | 2 + >>>>>>>> arch/powerpc/include/asm/kvm_ppc.h | 16 +- >>>>>>>> arch/powerpc/kvm/book3s_64_vio.c | 118 ++++++++++++++ >>>>>>>> arch/powerpc/kvm/book3s_64_vio_hv.c | 266 >>>>>>>> +++++++++++++++++++++++++++---- arch/powerpc/kvm/book3s_hv.c >>>>>>>> | 39 +++++ arch/powerpc/kvm/book3s_hv_rmhandlers.S | 6 + >>>>>>>> arch/powerpc/kvm/book3s_pr_papr.c | 37 ++++- >>>>>>>> arch/powerpc/kvm/powerpc.c | 3 + >>>>>>>> include/uapi/linux/kvm.h | 1 + 10 files >>>>>>>> changed, 473 insertions(+), 32 deletions(-) >>>>>>>> >>>>>>>> diff --git a/Documentation/virtual/kvm/api.txt >>>>>>>> b/Documentation/virtual/kvm/api.txt index 5f91eda..6c082ff >>>>>>>> 100644 --- a/Documentation/virtual/kvm/api.txt +++ >>>>>>>> b/Documentation/virtual/kvm/api.txt @@ -2362,6 +2362,23 @@ >>>>>>>> calls by the guest for that service will be passed to >>>>>>>> userspace to be handled. >>>>>>>> >>>>>>>> >>>>>>>> +4.83 KVM_CAP_PPC_MULTITCE + +Capability: >>>>>>>> KVM_CAP_PPC_MULTITCE +Architectures: ppc +Type: vm + +This >>>>>>>> capability tells the guest that multiple TCE entry add/remove >>>>>>>> hypercalls +handling is supported by the kernel. This >>>>>>>> significanly accelerates DMA +operations for PPC KVM guests. >>>>>>>> + +Unlike other capabilities in this section, this one does >>>>>>>> not have an ioctl. +Instead, when the capability is present, >>>>>>>> the H_PUT_TCE_INDIRECT and +H_STUFF_TCE hypercalls are to be >>>>>>>> handled in the host kernel and not passed to +the guest. >>>>>>>> Othwerwise it might be better for the guest to continue using >>>>>>>> H_PUT_TCE +hypercall (if KVM_CAP_SPAPR_TCE or >>>>>>>> KVM_CAP_SPAPR_TCE_IOMMU are present). >>>>>>> While this describes perfectly well what the consequences are of >>>>>>> the patches, it does not describe properly what the CAP actually >>>>>>> expresses. The CAP only says "this kernel is able to handle >>>>>>> H_PUT_TCE_INDIRECT and H_STUFF_TCE hypercalls directly". All >>>>>>> other consequences are nice to document, but the semantics of >>>>>>> the CAP are missing. >>>>>> >>>>>> ? It expresses ability to handle 2 hcalls. What is missing? >>>>> You don't describe the kvm<-> qemu interface. You describe some >>>>> decisions qemu can take from this cap. >>>> >>>> This file does not mention qemu at all. And the interface is - qemu >>>> (or kvmtool could do that) just adds "hcall-multi-tce" to >>>> "ibm,hypertas-functions" but this is for pseries linux and AIX could >>>> always do it (no idea about it). Does it really have to be in this >>>> file? >>> Ok, let's go back a step. What does this CAP describe? Don't look at >>> the >>> description you wrote above. Just write a new one. >> The CAP means the kernel is capable of handling hcalls A and B without >> passing those into the user space. That accelerates DMA. >> >> >>> What exactly can user space expect when it finds this CAP? >> The user space can expect that its handlers for A and B are not going >> to be >> called if it configures the guest appropriately. Actually a nitpick here too. User space can expect that its handlers for A and B are going to already be processed by KVM. Regardless of how user space configures the guest. Alex -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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