linux-kernel - Re: [PATCH v4 09/18] KVM: arm64: selftests: Add guest support to get the vcpuid

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Message-ID: <20210910081001.4gljsvmcovvoylwt@gator>
Date:   Fri, 10 Sep 2021 10:10:01 +0200
From:   Andrew Jones <drjones@...hat.com>
To:     Raghavendra Rao Ananta <rananta@...gle.com>
Cc:     Paolo Bonzini <pbonzini@...hat.com>, 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>, Peter Shier <pshier@...gle.com>,
        Ricardo Koller <ricarkol@...gle.com>,
        Oliver Upton <oupton@...gle.com>,
        Reiji Watanabe <reijiw@...gle.com>,
        Jing Zhang <jingzhangos@...gle.com>,
        linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Subject: Re: [PATCH v4 09/18] KVM: arm64: selftests: Add guest support to get
 the vcpuid

On Thu, Sep 09, 2021 at 10:10:56AM -0700, Raghavendra Rao Ananta wrote:
> On Thu, Sep 9, 2021 at 12:56 AM Andrew Jones <drjones@...hat.com> wrote:
> >
> > On Thu, Sep 09, 2021 at 01:38:09AM +0000, Raghavendra Rao Ananta wrote:
...
> > > +     for (i = 0; i < KVM_MAX_VCPUS; i++) {
> > > +             vcpuid = vcpuid_map[i].vcpuid;
> > > +             GUEST_ASSERT_1(vcpuid != VM_VCPUID_MAP_INVAL, mpidr);
> >
> > We don't want this assert if it's possible to have sparse maps, which
> > it probably isn't ever going to be, but...
> >
> If you look at the way the array is arranged, the element with
> VM_VCPUID_MAP_INVAL acts as a sentinel for us and all the proper
> elements would lie before this. So, I don't think we'd have a sparse
> array here.

If we switch to my suggestion of adding map entries at vcpu-add time and
removing them at vcpu-rm time, then the array may become sparse depending
on the order of removals.

Thanks,
drew