Re: [PATCH] KVM: x86: Increase KVM_MAX_VCPUS to 2048

[Vitaly Kuznetsov <vkuznets@redhat.com>]

Kyle Meyer <kyle.meyer@hpe.com> writes:

> Increase KVM_MAX_VCPUS to 2048 so we can run larger virtual machines.
>
> Notable changes:
>
> * KVM_CAP_MAX_VCPUS will return 2048.
> * KVM_MAX_VCPU_IDS will increase from 4096 to 8192.
> * KVM_HV_MAX_SPARSE_VCPU_SET_BITS will increase from 16 to 32.
>
> * CPUID[HYPERV_CPUID_IMPLEMENT_LIMITS (00x40000005)].EAX will now be 2048.
>
> * struct kvm will increase from 40336 B to 40464 B.
> * struct kvm_arch will increase from 34488 B to 34616 B.
> * struct kvm_ioapic will increase from 5240 B to 9848 B.
>
> * vcpu_mask in kvm_hv_flush_tlb will increase from 128 B to 256 B.
> * vcpu_mask in kvm_hv_send_ipi will increase from 128 B to 256 B.

FWIW, this one will go away when
https://lore.kernel.org/kvm/20220606083655.2014609-11-vkuznets@redhat.com/
lands.

> * vcpu_bitmap in ioapic_write_indirect will increase from 128 B to 256 B.
> * vp_bitmap in sparse_set_to_vcpu_mask will increase from 128 B to 256 B.

...

> * sparse_banks in kvm_hv_flush_tlb will increase from 128 B to 256 B.
> * sparse_banks in kvm_hv_send_ipi will increase from 128 B to 256 B.

and these two are going away with
https://lore.kernel.org/kvm/20220606083655.2014609-13-vkuznets@redhat.com/
(at the cost of growing 'struct kvm_vcpu_hv')

>
> Signed-off-by: Kyle Meyer <kyle.meyer@hpe.com>
> ---
>  arch/x86/include/asm/kvm_host.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 3a240a64ac68..58653c63899f 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -38,7 +38,7 @@
>  
>  #define __KVM_HAVE_ARCH_VCPU_DEBUGFS
>  
> -#define KVM_MAX_VCPUS 1024
> +#define KVM_MAX_VCPUS 2048
>  
>  /*
>   * In x86, the VCPU ID corresponds to the APIC ID, and APIC IDs

-- 
Vitaly