linux-kernel - Re: [PATCH 0/6] x86/kvm: add boot parameters for max vcpu configs

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Date:   Mon, 26 Jul 2021 15:41:09 +0200
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Juergen Gross <jgross@...e.com>, linux-kernel@...r.kernel.org,
        x86@...nel.org, kvm@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org
Cc:     Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, Jonathan Corbet <corbet@....net>,
        Marc Zyngier <maz@...nel.org>,
        James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>, kvmarm@...ts.cs.columbia.edu
Subject: Re: [PATCH 0/6] x86/kvm: add boot parameters for max vcpu configs

On 01/07/21 17:40, Juergen Gross wrote:
> In order to be able to have a single kernel for supporting even huge
> numbers of vcpus per guest some arrays should be sized dynamically.
> 
> The easiest way to do that is to add boot parameters for the maximum
> number of vcpus and the highest supported vcpu-id overwriting the
> normal default.
> 
> This patch series is doing that for x86. The same scheme can be easily
> adapted to other architectures, but I don't want to do that in the
> first iteration.
> 
> In the long term I'd suggest to have a per-guest setting of the two
> parameters allowing to spare some memory for smaller guests. OTOH this
> would require new ioctl()s and respective qemu modifications, so I let
> those away for now.
> 
> I've tested the series not to break normal guest operation and the new
> parameters to be effective on x86. For Arm64 I did a compile test only.
> 
> Juergen Gross (6):
>    x86/kvm: fix vcpu-id indexed array sizes
>    x86/kvm: remove non-x86 stuff from arch/x86/kvm/ioapic.h
>    x86/kvm: add boot parameter for maximum vcpu-id
>    x86/kvm: introduce per cpu vcpu masks
>    kvm: allocate vcpu pointer array separately
>    x86/kvm: add boot parameter for setting max number of vcpus per guest
> 
>   .../admin-guide/kernel-parameters.txt         | 18 +++++++
>   arch/arm64/kvm/arm.c                          | 28 +++++++++--
>   arch/x86/include/asm/kvm_host.h               | 22 ++++++---
>   arch/x86/kvm/hyperv.c                         | 25 +++++++---
>   arch/x86/kvm/ioapic.c                         | 14 +++++-
>   arch/x86/kvm/ioapic.h                         |  8 +--
>   arch/x86/kvm/irq_comm.c                       |  9 +++-
>   arch/x86/kvm/x86.c                            | 49 ++++++++++++++++++-
>   include/linux/kvm_host.h                      | 17 ++++++-
>   9 files changed, 160 insertions(+), 30 deletions(-)
> 

Queued patches 1-2, thanks (1 for stable too).

Paolo