linux-kernel - Re: [PATCH v2 5/6] KVM: s390: Cap KVM_CAP_NR_VCPUS by num_online

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Message-ID: <df5a43bb-3944-6fbb-a98f-94c46db867f8@linux.ibm.com>
Date:   Wed, 17 Nov 2021 08:33:38 +0100
From:   Christian Borntraeger <borntraeger@...ux.ibm.com>
To:     Vitaly Kuznetsov <vkuznets@...hat.com>, kvm@...r.kernel.org,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Eduardo Habkost <ehabkost@...hat.com>,
        Marc Zyngier <maz@...nel.org>,
        Andrew Jones <drjones@...hat.com>,
        Huacai Chen <chenhuacai@...nel.org>,
        Aleksandar Markovic <aleksandar.qemu.devel@...il.com>,
        Anup Patel <anup.patel@....com>,
        Paul Mackerras <paulus@...abs.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Janosch Frank <frankja@...ux.ibm.com>, kvm-ppc@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-mips@...r.kernel.org,
        kvm-riscv@...ts.infradead.org, linux-s390@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 5/6] KVM: s390: Cap KVM_CAP_NR_VCPUS by
 num_online_cpus()

Am 16.11.21 um 17:34 schrieb Vitaly Kuznetsov:
> KVM_CAP_NR_VCPUS is a legacy advisory value which on other architectures
> return num_online_cpus() caped by KVM_CAP_NR_VCPUS or something else
> (ppc and arm64 are special cases). On s390, KVM_CAP_NR_VCPUS returns
> the same as KVM_CAP_MAX_VCPUS and this may turn out to be a bad
> 'advice'. Switch s390 to returning caped num_online_cpus() too.
> 
> Acked-by: Christian Borntraeger <borntraeger@...ibm.com>

you can also add
Reviewed-by: Christian Borntraeger <borntraeger@...ux.ibm.com>

(yes I am changing my default address, but the other should continue to work)

> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
> ---
>   arch/s390/kvm/kvm-s390.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/arch/s390/kvm/kvm-s390.c b/arch/s390/kvm/kvm-s390.c
> index 6a6dd5e1daf6..1cfe36f6432e 100644
> --- a/arch/s390/kvm/kvm-s390.c
> +++ b/arch/s390/kvm/kvm-s390.c
> @@ -585,6 +585,8 @@ int kvm_vm_ioctl_check_extension(struct kvm *kvm, long ext)
>   			r = KVM_MAX_VCPUS;
>   		else if (sclp.has_esca && sclp.has_64bscao)
>   			r = KVM_S390_ESCA_CPU_SLOTS;
> +		if (ext == KVM_CAP_NR_VCPUS)
> +			r = min_t(unsigned int, num_online_cpus(), r);
>   		break;
>   	case KVM_CAP_S390_COW:
>   		r = MACHINE_HAS_ESOP;
>