On Wed, 4 May 2016 18:45:34 +0200 Radim Krčmář <rkrcmar@xxxxxxxxxx> wrote: > 2016-05-03 06:52+0200, Greg Kurz: > > The KVM_MAX_VCPUS define provides the maximum number of vCPUs per guest, and > > also the upper limit for vCPU ids. This is okay for all archs except PowerPC > > which can have higher ids, depending on the cpu/core/thread topology. In the > > worst case (single threaded guest, host with 8 threads per core), it limits > > the maximum number of vCPUS to KVM_MAX_VCPUS / 8. > > > > This patch separates the vCPU numbering from the total number of vCPUs, with > > the introduction of KVM_MAX_VCPU_ID, as the maximal valid value for vCPU ids > > plus one. > > > > The corresponding KVM_CAP_MAX_VCPU_ID allows userspace to validate vCPU ids > > before passing them to KVM_CREATE_VCPU. > > > > Only PowerPC gets unlimited vCPU ids for the moment. This patch doesn't > > change anything for other archs. > > > > Suggested-by: Radim Krcmar <rkrcmar@xxxxxxxxxx> > > Signed-off-by: Greg Kurz <gkurz@xxxxxxxxxxxxxxxxxx> > > --- > > diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c > > @@ -2272,7 +2272,7 @@ static int kvm_vm_ioctl_create_vcpu(struct kvm *kvm, u32 id) > > int r; > > struct kvm_vcpu *vcpu; > > > > - if (id >= KVM_MAX_VCPUS) > > + if (id >= KVM_MAX_VCPU_ID) > > return -EINVAL; > > book3s_hv will currently fail with vcpu_id above threads_per_subcore * > KVM_MAX_VCORES, so userspace cannot use KVM_CAP_MAX_VCPU_ID to limit > vcpu_id ... You're right, I guess powerpc should return threads_per_subcore * KVM_MAX_VCORES instead of INT_MAX then. > I thought the check for vcpu_id would move to arch-specific > code, like the previous version did, to simplify implementation of a > dynamic limit. > > The dynamic limit was too complicated to be worth it? > (This version is ok too.) > Actually no, it can be as simple as this in arch/powerpc/include/asm/kvm_host.h: #include <asm/cputhreads.h> #define KVM_MAX_VCPU_ID (threads_per_subcore * KVM_MAX_VCORES) Thanks ! -- Greg -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
