[PATCH v4 08/19] arm/arm64: KVM: make the maximum number of vCPUs a per-VM value
Andre Przywara
andre.przywara at arm.com
Mon Dec 8 06:10:47 PST 2014
Hi Christoffer,
On 23/11/14 13:21, Christoffer Dall wrote:
> On Fri, Nov 14, 2014 at 10:07:52AM +0000, Andre Przywara wrote:
>> Currently the maximum number of vCPUs supported is a global value
>> limited by the used GIC model. GICv3 will lift this limit, but we
>> still need to observe it for guests using GICv2.
>> So the maximum number of vCPUs is per-VM value, depending on the
>> GIC model the guest uses.
>> Store and check the value in struct kvm_arch, but keep it down to
>> 8 for now.
>>
>> Signed-off-by: Andre Przywara <andre.przywara at arm.com>
>> ---
>> Changelog v3...v4:
>> - initialize max_vcpus with limit based on host GIC
>> - remove *_init_emul_* from VGIC backend
>> - refine VCPU limit on VGIC creation
>> - print warning when userland tries to create more VCPUs than supported
>>
>> arch/arm/include/asm/kvm_host.h | 1 +
>> arch/arm/kvm/arm.c | 8 ++++++++
>> arch/arm64/include/asm/kvm_host.h | 3 +++
>> include/kvm/arm_vgic.h | 2 ++
>> virt/kvm/arm/vgic-v2.c | 1 +
>> virt/kvm/arm/vgic-v3.c | 1 +
>> virt/kvm/arm/vgic.c | 22 ++++++++++++++++++++++
>> 7 files changed, 38 insertions(+)
>>
>> diff --git a/arch/arm/include/asm/kvm_host.h b/arch/arm/include/asm/kvm_host.h
>> index b443dfe..7969e6e 100644
>> --- a/arch/arm/include/asm/kvm_host.h
>> +++ b/arch/arm/include/asm/kvm_host.h
>> @@ -68,6 +68,7 @@ struct kvm_arch {
>>
>> /* Interrupt controller */
>> struct vgic_dist vgic;
>> + int max_vcpus;
>> };
>>
>> #define KVM_NR_MEM_OBJS 40
>> diff --git a/arch/arm/kvm/arm.c b/arch/arm/kvm/arm.c
>> index 8817fbd..c3d0fbd 100644
>> --- a/arch/arm/kvm/arm.c
>> +++ b/arch/arm/kvm/arm.c
>> @@ -132,6 +132,9 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
>> /* Mark the initial VMID generation invalid */
>> kvm->arch.vmid_gen = 0;
>>
>> + /* The maximum number of VCPUs is limited by the host's GIC model */
>> + kvm->arch.max_vcpus = kvm_vgic_get_max_vcpus();
>
> I think you forgot to declare this one in arm_vgic.h for
> v7-without-vgic-but-with-kvm-configure-case
> (which-we-should-have-gotten-rid-of-a-while-back-perhaps).
Ah yes, thanks for pointing this out. Fixed in v5.
>> +
>> return ret;
>> out_free_stage2_pgd:
>> kvm_free_stage2_pgd(kvm);
>> @@ -213,6 +216,11 @@ struct kvm_vcpu *kvm_arch_vcpu_create(struct kvm *kvm, unsigned int id)
>> int err;
>> struct kvm_vcpu *vcpu;
>>
>> + if (id >= kvm->arch.max_vcpus) {
>> + err = -EINVAL;
>> + goto out;
>> + }
>> +
>> vcpu = kmem_cache_zalloc(kvm_vcpu_cache, GFP_KERNEL);
>> if (!vcpu) {
>> err = -ENOMEM;
>> diff --git a/arch/arm64/include/asm/kvm_host.h b/arch/arm64/include/asm/kvm_host.h
>> index 286bb61..f9e130d 100644
>> --- a/arch/arm64/include/asm/kvm_host.h
>> +++ b/arch/arm64/include/asm/kvm_host.h
>> @@ -59,6 +59,9 @@ struct kvm_arch {
>> /* VTTBR value associated with above pgd and vmid */
>> u64 vttbr;
>>
>> + /* The maximum number of vCPUs depends on the used GIC model */
>> + int max_vcpus;
>> +
>> /* Interrupt controller */
>> struct vgic_dist vgic;
>>
>> diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
>> index bfb660a..09344ac 100644
>> --- a/include/kvm/arm_vgic.h
>> +++ b/include/kvm/arm_vgic.h
>> @@ -132,6 +132,7 @@ struct vgic_params {
>> unsigned int maint_irq;
>> /* Virtual control interface base address */
>> void __iomem *vctrl_base;
>> + int max_hw_vcpus;
>
> nit: max_vcpus or max_gic_vcpus would be more meaningful imho.
Sure.
>> };
>>
>> struct vgic_vm_ops {
>> @@ -287,6 +288,7 @@ struct kvm_exit_mmio;
>> #ifdef CONFIG_KVM_ARM_VGIC
>> int kvm_vgic_addr(struct kvm *kvm, unsigned long type, u64 *addr, bool write);
>> int kvm_vgic_hyp_init(void);
>> +int kvm_vgic_get_max_vcpus(void);
>> int kvm_vgic_init(struct kvm *kvm);
>> int kvm_vgic_create(struct kvm *kvm, u32 type);
>> void kvm_vgic_destroy(struct kvm *kvm);
>> diff --git a/virt/kvm/arm/vgic-v2.c b/virt/kvm/arm/vgic-v2.c
>> index e1cd3cb..49fb288 100644
>> --- a/virt/kvm/arm/vgic-v2.c
>> +++ b/virt/kvm/arm/vgic-v2.c
>> @@ -237,6 +237,7 @@ int vgic_v2_probe(struct device_node *vgic_node,
>> vctrl_res.start, vgic->maint_irq);
>>
>> vgic->type = VGIC_V2;
>> + vgic->max_hw_vcpus = 8;
>
> define GIC_V2_MAX_CPUS ?
Yes, makes sense.
>> *ops = &vgic_v2_ops;
>> *params = vgic;
>> goto out;
>> diff --git a/virt/kvm/arm/vgic-v3.c b/virt/kvm/arm/vgic-v3.c
>> index d14c75f..acd256c7 100644
>> --- a/virt/kvm/arm/vgic-v3.c
>> +++ b/virt/kvm/arm/vgic-v3.c
>> @@ -235,6 +235,7 @@ int vgic_v3_probe(struct device_node *vgic_node,
>> vgic->vcpu_base = vcpu_res.start;
>> vgic->vctrl_base = NULL;
>> vgic->type = VGIC_V3;
>> + vgic->max_hw_vcpus = KVM_MAX_VCPUS;
>>
>> kvm_info("%s@%llx IRQ%d\n", vgic_node->name,
>> vcpu_res.start, vgic->maint_irq);
>> diff --git a/virt/kvm/arm/vgic.c b/virt/kvm/arm/vgic.c
>> index 4aa0b2f..4c72c66 100644
>> --- a/virt/kvm/arm/vgic.c
>> +++ b/virt/kvm/arm/vgic.c
>> @@ -1841,6 +1841,17 @@ static int vgic_vcpu_init_maps(struct kvm_vcpu *vcpu, int nr_irqs)
>> }
>>
>> /**
>> + * kvm_vgic_get_max_vcpus - Get the maximum number of VCPUs allowed by HW
>> + *
>> + * The host's GIC naturally limits the maximum amount of VCPUs a guest
>> + * can use.
>> + */
>> +int kvm_vgic_get_max_vcpus(void)
>> +{
>> + return vgic->max_hw_vcpus;
>> +}
>> +
>> +/**
>> * kvm_vgic_vcpu_init - Initialize per-vcpu VGIC state
>> * @vcpu: pointer to the vcpu struct
>> *
>> @@ -2056,6 +2067,8 @@ static int vgic_v2_init_emulation(struct kvm *kvm)
>> dist->vm_ops.add_sgi_source = vgic_v2_add_sgi_source;
>> dist->vm_ops.vgic_init = vgic_v2_init;
>>
>> + kvm->arch.max_vcpus = 8;
>
> reuse the define here
>
>> +
>> return 0;
>> }
>>
>> @@ -2072,6 +2085,15 @@ static int init_vgic_model(struct kvm *kvm, int type)
>> break;
>> }
>>
>> + if (ret)
>> + return ret;
>> +
>> + if (kvm->arch.max_vcpus < atomic_read(&kvm->online_vcpus)) {
>
> I would invert this check; if (online_vcpus > max_vcpus) ...
Done.
>> + pr_warn_ratelimited("VGIC model only supports up to %d vCPUs\n",
>> + kvm->arch.max_vcpus);
>> + ret = -EINVAL;
>> + }
>> +
>> return ret;
>> }
>>
>> --
>> 1.7.9.5
>>
>
> So let me see if I got this right:
>
> When you create the VM you set the maximum number of vcpus to whatever
> the underlying vgic hardware allows.
>
> Then, when you start creating vcpus, you complain if the user tries to
> create more than what the hardware allows (check against
> kvm->arch.max_vcpus).
>
> Then, when you create the vgic, you further limit kvm->arch.max_vcpus
> and check if you already created too many vcpus for the vgic model you
> are trying to create, and error out in that case, and now also check
> against the new value when user space is trying to create more vcpus.
Yes, that was my idea.
> Some questions:
>
> (1) Is there currently a way to tell user space what the maximum number
> of vcpus for a given setup is?
Not that I know of (also not for the other architectures, AFAICT).
I guess we would inherit that possible change of the result when doing
the ioctl before or after the VGIC creation, so I am not sure if that is
really a useful ioctl to have. Maybe as part of the VGIC kvm_device
interface, which would automatically ensure only one answer?
> (2) Would it be simpler to just have kvm_vgic_max_vcpus() return its
> best guess and always check against that from the outside? Hmmm, maybe
> not, but thought I'd throw it out there.
Maybe, maybe not, lets make this a separate bikeshed discussion right
before the holidays ;-)
Cheers,
Andre.
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