From: Marc Zyngier <maz@kernel.org>
To: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
kvm@vger.kernel.org, Sean Christopherson <seanjc@google.com>,
Wanpeng Li <wanpengli@tencent.com>,
Jim Mattson <jmattson@google.com>,
Eduardo Habkost <ehabkost@redhat.com>,
Andrew Jones <drjones@redhat.com>,
Huacai Chen <chenhuacai@kernel.org>,
Aleksandar Markovic <aleksandar.qemu.devel@gmail.com>,
Anup Patel <anup.patel@wdc.com>,
Paul Mackerras <paulus@ozlabs.org>,
Michael Ellerman <mpe@ellerman.id.au>,
kvm-ppc@vger.kernel.org, linux-arm-kernel@lists.infradead.org,
linux-mips@vger.kernel.org, kvm-riscv@lists.infradead.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/5] KVM: arm64: Cap KVM_CAP_NR_VCPUS by KVM_CAP_MAX_VCPUS
Date: Tue, 16 Nov 2021 15:55:11 +0000 [thread overview]
Message-ID: <875yss859c.wl-maz@kernel.org> (raw)
In-Reply-To: <87y25onsj6.fsf@redhat.com>
On Tue, 16 Nov 2021 13:23:25 +0000,
Vitaly Kuznetsov <vkuznets@redhat.com> wrote:
>
> Paolo Bonzini <pbonzini@redhat.com> writes:
>
> > On 11/12/21 15:02, Marc Zyngier wrote:
> >>> I'd like KVM to be consistent across architectures and have the same
> >>> (similar) meaning for KVM_CAP_NR_VCPUS.
> >> Sure, but this is a pretty useless piece of information anyway. As
> >> Andrew pointed out, the information is available somewhere else, and
> >> all we need to do is to cap it to the number of supported vcpus, which
> >> is effectively a KVM limitation.
> >>
> >> Also, we are talking about representing the architecture to userspace.
> >> No amount of massaging is going to make an arm64 box look like an x86.
> >
> > Not sure what you mean? The API is about providing a piece of
> > information independent of the architecture, while catering for a ppc
> > weirdness. Yes it's mostly useless if you don't care about ppc, but
> > it's not about making arm64 look like x86 or ppc; it's about not having
> > to special case ppc in userspace.
> >
> > If anything, if KVM_CAP_NR_VCPUS returns the same for kvm and !kvm, then
> > *that* is making an arm64 box look like an x86. On ARM the max vCPUs
> > depends on VM's GIC configuration, so KVM_CAP_NR_VCPUS should take that
> > into account.
>
> (I'm about to send v2 as we have s390 sorted out.)
>
> So what do we decide about ARM?
[...]
> - Always kvm_arm_default_max_vcpus to make the output independent on 'if
> (kvm)'.
This. Between two useless numbers, I prefer the one that doesn't
introduce any userspace visible changes.
Thanks,
M.
--
Without deviation from the norm, progress is not possible.
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next prev parent reply other threads:[~2021-11-16 15:57 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-11-11 16:27 [PATCH 0/5] KVM: Cap KVM_CAP_NR_VCPUS by KVM_CAP_MAX_VCPUS and re-purpose it on x86 Vitaly Kuznetsov
2021-11-11 16:27 ` [PATCH 1/5] KVM: arm64: Cap KVM_CAP_NR_VCPUS by KVM_CAP_MAX_VCPUS Vitaly Kuznetsov
2021-11-11 19:36 ` Marc Zyngier
2021-11-12 9:51 ` Vitaly Kuznetsov
2021-11-12 10:38 ` Andrew Jones
2021-11-12 10:51 ` Paolo Bonzini
2021-11-12 14:02 ` Marc Zyngier
2021-11-12 14:10 ` Paolo Bonzini
2021-11-16 13:23 ` Vitaly Kuznetsov
2021-11-16 15:50 ` Paolo Bonzini
2021-11-16 15:55 ` Marc Zyngier [this message]
2021-11-16 15:58 ` Paolo Bonzini
2021-11-11 16:27 ` [PATCH 2/5] KVM: MIPS: " Vitaly Kuznetsov
2021-11-11 16:27 ` [PATCH 3/5] KVM: PPC: " Vitaly Kuznetsov
2021-11-11 16:27 ` [PATCH 4/5] KVM: RISC-V: " Vitaly Kuznetsov
2021-11-11 16:27 ` [PATCH 5/5] KVM: x86: Drop arbitraty KVM_SOFT_MAX_VCPUS Vitaly Kuznetsov
2021-11-11 16:32 ` [PATCH 0/5] KVM: Cap KVM_CAP_NR_VCPUS by KVM_CAP_MAX_VCPUS and re-purpose it on x86 Paolo Bonzini
2021-11-15 12:16 ` Christian Borntraeger
2021-11-15 12:33 ` Christian Borntraeger
2021-11-15 16:04 ` Vitaly Kuznetsov
2021-11-16 8:15 ` Christian Borntraeger
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