linux-kernel - Re: [PATCH v5.5 05/30] KVM: Resync only arch fields when slots_arch

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Message-ID: <aae78856-6a7b-6812-029a-32ddb6ad6866@oracle.com>
Date:   Tue, 9 Nov 2021 01:38:47 +0100
From:   "Maciej S. Szmigiero" <maciej.szmigiero@...cle.com>
To:     Sean Christopherson <seanjc@...gle.com>
Cc:     James Morse <james.morse@....com>,
        Alexandru Elisei <alexandru.elisei@....com>,
        Suzuki K Poulose <suzuki.poulose@....com>,
        Atish Patra <atish.patra@....com>,
        David Hildenbrand <david@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Claudio Imbrenda <imbrenda@...ux.ibm.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-mips@...r.kernel.org, kvm@...r.kernel.org,
        kvm-ppc@...r.kernel.org, kvm-riscv@...ts.infradead.org,
        linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Ben Gardon <bgardon@...gle.com>, Marc Zyngier <maz@...nel.org>,
        Huacai Chen <chenhuacai@...nel.org>,
        Aleksandar Markovic <aleksandar.qemu.devel@...il.com>,
        Paul Mackerras <paulus@...abs.org>,
        Anup Patel <anup.patel@....com>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmer@...belt.com>,
        Albert Ou <aou@...s.berkeley.edu>,
        Christian Borntraeger <borntraeger@...ibm.com>,
        Janosch Frank <frankja@...ux.ibm.com>,
        Paolo Bonzini <pbonzini@...hat.com>
Subject: Re: [PATCH v5.5 05/30] KVM: Resync only arch fields when
 slots_arch_lock gets reacquired

On 04.11.2021 01:25, Sean Christopherson wrote:
> From: Maciej S. Szmigiero <maciej.szmigiero@...cle.com>
> 
> There is no need to copy the whole memslot data after releasing
> slots_arch_lock for a moment to install temporary memslots copy in
> kvm_set_memslot() since this lock only protects the arch field of each
> memslot.
> 
> Just resync this particular field after reacquiring slots_arch_lock.
> 
> Note, this also eliminates the need to manually clear the INVALID flag
> when restoring memslots; the "setting" of the INVALID flag was an
> unwanted side effect of copying the entire memslots.
> 
> Signed-off-by: Maciej S. Szmigiero <maciej.szmigiero@...cle.com>
> [sean: tweak shortlog, note INVALID flag in changelog, revert comment]

This updated patch also open-codes kvm_copy_memslots(), which my
previous version didn't.
I think it's worth mentioning this in the change log, too.

Thanks,
Maciej