linux-kernel - [PATCH v2 0/6] x86/kvm: add boot parameters for max vcpu configs

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Message-Id: <20210903130808.30142-1-jgross@suse.com>
Date:   Fri,  3 Sep 2021 15:08:01 +0200
From:   Juergen Gross <jgross@...e.com>
To:     kvm@...r.kernel.org, x86@...nel.org, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Cc:     maz@...nel.org, ehabkost@...hat.com,
        Juergen Gross <jgross@...e.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        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>,
        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: [PATCH v2 0/6] x86/kvm: add boot parameters for max vcpu configs

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 to calculate the maximum vcpu-id from that using
either the host topology or a topology hint via another boot parameter.

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.

Changes in V2:
- removed old patch 1, as already applied
- patch 1 (old patch 2) only for reference, as the patch is already in
  the kvm tree
- switch patch 2 (old patch 3) to calculate vcpu-id
- added patch 4

Juergen Gross (6):
  x86/kvm: remove non-x86 stuff from arch/x86/kvm/ioapic.h
  x86/kvm: add boot parameter for adding vcpu-id bits
  x86/kvm: introduce per cpu vcpu masks
  kvm: use kvfree() in kvm_arch_free_vm()
  kvm: allocate vcpu pointer array separately
  x86/kvm: add boot parameter for setting max number of vcpus per guest

 .../admin-guide/kernel-parameters.txt         | 25 ++++++
 arch/arm64/include/asm/kvm_host.h             |  1 -
 arch/arm64/kvm/arm.c                          | 23 ++++--
 arch/x86/include/asm/kvm_host.h               | 26 +++++--
 arch/x86/kvm/hyperv.c                         | 25 ++++--
 arch/x86/kvm/ioapic.c                         | 12 ++-
 arch/x86/kvm/ioapic.h                         |  8 +-
 arch/x86/kvm/irq_comm.c                       |  9 ++-
 arch/x86/kvm/x86.c                            | 78 ++++++++++++++++++-
 include/linux/kvm_host.h                      | 26 ++++++-
 10 files changed, 198 insertions(+), 35 deletions(-)

-- 
2.26.2