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Re: [PATCH 4/4] KVM: x86: enable configurable MAX_VCPU

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2017-04-19 10:08+0200, Christian Borntraeger:
> On 04/13/2017 10:19 PM, Radim Krčmář wrote:
>> The only user of KVM_MAX_VCPU is switched to kvm->max_vcpu.
>> 
>> The limit could have been INT_MAX as it makes no difference, but there
>> is no point in making it bigger than KVM_MAX_VCPU_ID.
>> 
>> Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>
>> ---
>>  arch/x86/include/asm/kvm_host.h | 1 +
>>  arch/x86/kvm/irq_comm.c         | 4 ++--
>>  2 files changed, 3 insertions(+), 2 deletions(-)
>> 
>> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
>> index 2cc5ec7cc6f5..eeeb88eedabf 100644
>> --- a/arch/x86/include/asm/kvm_host.h
>> +++ b/arch/x86/include/asm/kvm_host.h
>> @@ -38,6 +38,7 @@
>>  #define KVM_MAX_VCPUS 288
>>  #define KVM_SOFT_MAX_VCPUS 240
>>  #define KVM_MAX_VCPU_ID 1023
>> +#define KVM_CONFIGURABLE_MAX_VCPUS KVM_MAX_VCPU_ID
>>  #define KVM_USER_MEM_SLOTS 509
>>  /* memory slots that are not exposed to userspace */
>>  #define KVM_PRIVATE_MEM_SLOTS 3
>> diff --git a/arch/x86/kvm/irq_comm.c b/arch/x86/kvm/irq_comm.c
>> index 4517a4c2ac3a..a7baeb44539a 100644
>> --- a/arch/x86/kvm/irq_comm.c
>> +++ b/arch/x86/kvm/irq_comm.c
>> @@ -60,7 +60,7 @@ int kvm_irq_delivery_to_apic(struct kvm *kvm, struct kvm_lapic *src,
>>  {
>>  	int i, r = -1;
>>  	struct kvm_vcpu *vcpu, *lowest = NULL;
>> -	unsigned long dest_vcpu_bitmap[BITS_TO_LONGS(KVM_MAX_VCPUS)];
>> +	unsigned long dest_vcpu_bitmap[BITS_TO_LONGS(kvm->max_vcpus)];
> 
> Doesnt that allow unlimited stack usage?

Right, it doesn't scale.

kvm->max_vcpus is at most KVM_CONFIGURABLE_MAX_VCPUS, but that will be
bigger than the stack.  I'll allocate the bitmap in v2.

Thanks.

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[PATCH 0/4] KVM: add KVM_CREATE_VM2 to allow dynamic kvm->vcpus array Radim Krčmář <rkrcmar@redhat.com> - 2017-04-13 22:30 +0200
  [PATCH 4/4] KVM: x86: enable configurable MAX_VCPU Radim Krčmář <rkrcmar@redhat.com> - 2017-04-13 22:30 +0200
    Re: [PATCH 4/4] KVM: x86: enable configurable MAX_VCPU Christian Borntraeger <borntraeger@de.ibm.com> - 2017-04-19 10:10 +0200
      Re: [PATCH 4/4] KVM: x86: enable configurable MAX_VCPU Radim Krčmář <rkrcmar@redhat.com> - 2017-04-24 19:10 +0200
  [PATCH 2/4] KVM: allocate kvm->vcpus separately Radim Krčmář <rkrcmar@redhat.com> - 2017-04-13 22:30 +0200
  [PATCH 1/4] KVM: remove unused __KVM_HAVE_ARCH_VM_ALLOC Radim Krčmář <rkrcmar@redhat.com> - 2017-04-13 22:30 +0200
    Re: [PATCH 1/4] KVM: remove unused __KVM_HAVE_ARCH_VM_ALLOC David Hildenbrand <david@redhat.com> - 2017-04-18 13:00 +0200
  [PATCH 3/4] KVM: add KVM_CREATE_VM2 system ioctl Radim Krčmář <rkrcmar@redhat.com> - 2017-04-13 22:30 +0200
    Re: [PATCH 3/4] KVM: add KVM_CREATE_VM2 system ioctl Paolo Bonzini <pbonzini@redhat.com> - 2017-04-18 16:20 +0200
      Re: [PATCH 3/4] KVM: add KVM_CREATE_VM2 system ioctl Paolo Bonzini <pbonzini@redhat.com> - 2017-04-18 16:40 +0200
        Re: [PATCH 3/4] KVM: add KVM_CREATE_VM2 system ioctl Radim Krčmář <rkrcmar@redhat.com> - 2017-04-24 18:30 +0200
          Re: [PATCH 3/4] KVM: add KVM_CREATE_VM2 system ioctl Radim Krčmář <rkrcmar@redhat.com> - 2017-04-24 22:30 +0200
  Re: [PATCH 0/4] KVM: add KVM_CREATE_VM2 to allow dynamic kvm->vcpus  array David Hildenbrand <david@redhat.com> - 2017-04-18 13:20 +0200
    Re: [PATCH 0/4] KVM: add KVM_CREATE_VM2 to allow dynamic kvm->vcpus  array Cornelia Huck <cornelia.huck@de.ibm.com> - 2017-04-18 14:30 +0200
      Re: [PATCH 0/4] KVM: add KVM_CREATE_VM2 to allow dynamic kvm->vcpus  array Radim Krčmář <rkrcmar@redhat.com> - 2017-04-24 22:10 +0200
    Re: [PATCH 0/4] KVM: add KVM_CREATE_VM2 to allow dynamic kvm->vcpus  array Radim Krčmář <rkrcmar@redhat.com> - 2017-04-24 19:10 +0200

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