On Tue, May 01, 2018 at 02:52:21PM +1000, Sam Bobroff wrote: > On Tue, Apr 24, 2018 at 01:48:25PM +1000, David Gibson wrote: > > On Tue, Apr 24, 2018 at 01:19:15PM +1000, Sam Bobroff wrote: > > > On Mon, Apr 23, 2018 at 11:06:35AM +0200, Cédric Le Goater wrote: > > > > On 04/16/2018 06:09 AM, David Gibson wrote: [snip] > > > At the moment, kvm->vcores[] and xive->vp_base are both sized by NR_CPUS > > > (via KVM_MAX_VCPUS and KVM_MAX_VCORES which are both NR_CPUS). This is > > > enough space for the maximum number of VCPUs, and some space is wasted > > > when the guest uses less than this (but KVM doesn't know how many will > > > be created, so we can't do better easily). The problem is that the > > > indicies overflow before all of those VCPUs can be created, not that > > > more space is needed. > > > > > > We could fix the overflow by expanding these areas to KVM_MAX_VCPU_ID > > > but that will use 8x the space we use now, and we know that no more than > > > KVM_MAX_VCPUS will be used so all this new space is basically wasted. > > > > > > So remapping seems better if it will work. (Ben H. was strongly against > > > wasting more XIVE space if possible.) > > > > Hm, ok. Are the relevant arrays here per-VM, or global? Or some of both? > > Per-VM. They are the kvm->vcores[] array and the blocks of memory > pointed to by xive->vp_base. Hm. If it were global (where you can't know the size of a specific VM) I'd certainly see the concern about not expanding the size of the array. As it is, I'm a little perplexed that we care so much about the difference between KVM_MAX_VCPUS and KVM_MAX_VCPU_ID, a factor of 8, when we apparently don't care about the difference between the vm's actual number of cpus and KVM_MAX_VCPUS, a factor of maybe 2048 (for a 1vcpu guest and powernv_defconfig). > > > > In short, remapping provides a way to allow the guest to create it's full set > > > of VCPUs without wasting any more space than we do currently, without > > > having to do something more complicated like tracking used IDs or adding > > > additional KVM CAPs. > > > > > > > >> + > > > > >> #endif /* __ASM_KVM_BOOK3S_H__ */ > > > > >> diff --git a/arch/powerpc/kvm/book3s_hv.c b/arch/powerpc/kvm/book3s_hv.c > > > > >> index 9cb9448163c4..49165cc90051 100644 > > > > >> --- a/arch/powerpc/kvm/book3s_hv.c > > > > >> +++ b/arch/powerpc/kvm/book3s_hv.c > > > > >> @@ -1762,7 +1762,7 @@ static int threads_per_vcore(struct kvm *kvm) > > > > >> return threads_per_subcore; > > > > >> } > > > > >> > > > > >> -static struct kvmppc_vcore *kvmppc_vcore_create(struct kvm *kvm, int core) > > > > >> +static struct kvmppc_vcore *kvmppc_vcore_create(struct kvm *kvm, int id) > > > > >> { > > > > >> struct kvmppc_vcore *vcore; > > > > >> > > > > >> @@ -1776,7 +1776,7 @@ static struct kvmppc_vcore *kvmppc_vcore_create(struct kvm *kvm, int core) > > > > >> init_swait_queue_head(&vcore->wq); > > > > >> vcore->preempt_tb = TB_NIL; > > > > >> vcore->lpcr = kvm->arch.lpcr; > > > > >> - vcore->first_vcpuid = core * kvm->arch.smt_mode; > > > > >> + vcore->first_vcpuid = id; > > > > >> vcore->kvm = kvm; > > > > >> INIT_LIST_HEAD(&vcore->preempt_list); > > > > >> > > > > >> @@ -1992,12 +1992,18 @@ static struct kvm_vcpu *kvmppc_core_vcpu_create_hv(struct kvm *kvm, > > > > >> mutex_lock(&kvm->lock); > > > > >> vcore = NULL; > > > > >> err = -EINVAL; > > > > >> - core = id / kvm->arch.smt_mode; > > > > >> + if (cpu_has_feature(CPU_FTR_ARCH_300)) { > > > > >> + BUG_ON(kvm->arch.smt_mode != 1); > > > > >> + core = kvmppc_pack_vcpu_id(kvm, id); > > > > >> + } else { > > > > >> + core = id / kvm->arch.smt_mode; > > > > >> + } > > > > >> if (core < KVM_MAX_VCORES) { > > > > >> vcore = kvm->arch.vcores[core]; > > > > >> + BUG_ON(cpu_has_feature(CPU_FTR_ARCH_300) && vcore); > > > > >> if (!vcore) { > > > > >> err = -ENOMEM; > > > > >> - vcore = kvmppc_vcore_create(kvm, core); > > > > >> + vcore = kvmppc_vcore_create(kvm, id & ~(kvm->arch.smt_mode - 1)); > > > > >> kvm->arch.vcores[core] = vcore; > > > > >> kvm->arch.online_vcores++; > > > > >> } > > > > >> diff --git a/arch/powerpc/kvm/book3s_xive.c b/arch/powerpc/kvm/book3s_xive.c > > > > >> index f9818d7d3381..681dfe12a5f3 100644 > > > > >> --- a/arch/powerpc/kvm/book3s_xive.c > > > > >> +++ b/arch/powerpc/kvm/book3s_xive.c > > > > >> @@ -317,6 +317,11 @@ static int xive_select_target(struct kvm *kvm, u32 *server, u8 prio) > > > > >> return -EBUSY; > > > > >> } > > > > >> > > > > >> +static u32 xive_vp(struct kvmppc_xive *xive, u32 server) > > > > >> +{ > > > > >> + return xive->vp_base + kvmppc_pack_vcpu_id(xive->kvm, server); > > > > >> +} > > > > >> + > > > > > > > > > > I'm finding the XIVE indexing really baffling. There are a bunch of > > > > > other places where the code uses (xive->vp_base + NUMBER) directly. > > > > > > Ugh, yes. It looks like I botched part of my final cleanup and all the > > > cases you saw in kvm/book3s_xive.c should have been replaced with a call to > > > xive_vp(). I'll fix it and sorry for the confusion. > > > > Ok. > > > > > > This links the QEMU vCPU server NUMBER to a XIVE virtual processor number > > > > in OPAL. So we need to check that all used NUMBERs are, first, consistent > > > > and then, in the correct range. > > > > > > Right. My approach was to allow XIVE to keep using server numbers that > > > are equal to VCPU IDs, and just pack down the ID before indexing into > > > the vp_base area. > > > > > > > > If those are host side references, I guess they don't need updates for > > > > > this. > > > > > > These are all guest side references. > > > > > > > > But if that's the case, then how does indexing into the same array > > > > > with both host and guest server numbers make sense? > > > > > > Right, it doesn't make sense to mix host and guest server numbers when > > > we're remapping only the guest ones, but in this case (without native > > > guest XIVE support) it's just guest ones. > > > > Right. Will this remapping be broken by guest-visible XIVE? That is > > for the guest visible XIVE are we going to need to expose un-remapped > > XIVE server IDs to the guest? > > I'm not sure, I'll start looking at that next. > > > > > yes. VPs are allocated with KVM_MAX_VCPUS : > > > > > > > > xive->vp_base = xive_native_alloc_vp_block(KVM_MAX_VCPUS); > > > > > > > > but > > > > > > > > #define KVM_MAX_VCPU_ID (threads_per_subcore * KVM_MAX_VCORES) > > > > > > > > WE would need to change the allocation of the VPs I guess. > > > > > > Yes, this is one of the structures that overflow if we don't pack the IDs. > > > > > > > >> static u8 xive_lock_and_mask(struct kvmppc_xive *xive, > > > > >> struct kvmppc_xive_src_block *sb, > > > > >> struct kvmppc_xive_irq_state *state) > > > > >> @@ -1084,7 +1089,7 @@ int kvmppc_xive_connect_vcpu(struct kvm_device *dev, > > > > >> pr_devel("Duplicate !\n"); > > > > >> return -EEXIST; > > > > >> } > > > > >> - if (cpu >= KVM_MAX_VCPUS) { > > > > >> + if (cpu >= KVM_MAX_VCPU_ID) {>> > > > > >> pr_devel("Out of bounds !\n"); > > > > >> return -EINVAL; > > > > >> } > > > > >> @@ -1098,7 +1103,7 @@ int kvmppc_xive_connect_vcpu(struct kvm_device *dev, > > > > >> xc->xive = xive; > > > > >> xc->vcpu = vcpu; > > > > >> xc->server_num = cpu; > > > > >> - xc->vp_id = xive->vp_base + cpu; > > > > >> + xc->vp_id = xive_vp(xive, cpu); > > > > >> xc->mfrr = 0xff; > > > > >> xc->valid = true; > > > > >> > > > > > > > > > > > > > > > > > -- David Gibson | I'll have my music baroque, and my code david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_ | _way_ _around_! http://www.ozlabs.org/~dgibson