linux-kernel - Re: [PATCH 4/4] KVM: x86: enable configurable MAX

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Date:   Wed, 19 Apr 2017 10:08:58 +0200
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     Radim Krčmář <rkrcmar@...hat.com>,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Christoffer Dall <cdall@...aro.org>,
        Marc Zyngier <marc.zyngier@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Cornelia Huck <cornelia.huck@...ibm.com>,
        James Hogan <james.hogan@...tec.com>,
        Paul Mackerras <paulus@...abs.org>,
        Alexander Graf <agraf@...e.com>
Subject: Re: [PATCH 4/4] KVM: x86: enable configurable MAX_VCPU

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@...hat.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?