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From:   Raghavendra Rao Ananta <rananta@google.com>
Date:   Mon, 13 Sep 2021 09:51:35 -0700
Message-ID: <CAJHc60wVJP4=s3r16nLWXA8o=k71OagvLFrWVWwJJnLycHMQyw@mail.gmail.com>
Subject: Re: [PATCH v4 09/18] KVM: arm64: selftests: Add guest support to get
 the vcpuid
To:     Andrew Jones <drjones@redhat.com>
Cc:     Reiji Watanabe <reijiw@google.com>,
        Paolo Bonzini <pbonzini@redhat.com>,
        Marc Zyngier <maz@kernel.org>,
        James Morse <james.morse@arm.com>,
        Alexandru Elisei <alexandru.elisei@arm.com>,
        Suzuki K Poulose <suzuki.poulose@arm.com>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will@kernel.org>, Peter Shier <pshier@google.com>,
        Ricardo Koller <ricarkol@google.com>,
        Oliver Upton <oupton@google.com>,
        Jing Zhang <jingzhangos@google.com>,
        linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu,
        linux-kernel@vger.kernel.org, kvm@vger.kernel.org
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On Mon, Sep 13, 2021 at 12:35 AM Andrew Jones <drjones@redhat.com> wrote:
>
> On Sun, Sep 12, 2021 at 12:05:22AM -0700, Reiji Watanabe wrote:
> > Hi Raghu and all,
> >
> > On Wed, Sep 8, 2021 at 6:38 PM Raghavendra Rao Ananta
> > <rananta@google.com> wrote:
> > >
> > > At times, such as when in the interrupt handler, the guest wants
> > > to get the vcpuid that it's running on. As a result, introduce
> > > get_vcpuid() that returns the vcpuid of the calling vcpu. At its
> > > backend, the VMM prepares a map of vcpuid and mpidr during VM
> > > initialization and exports the map to the guest for it to read.
> >
> > How about using TPIDR_EL1 to hold the vcpuid ?
> > i.e. have aarch64_vcpu_setup() set the register to vcpuid and
> > guest_get_vcpuid() simply return a value of the register.
> > This would be a simpler solution to implement.
>
> That is a great suggestion. It's arch-specific, but maybe the
> other architectures can mimic it with their own capabilities.
> And, in the unlikely event a unit test wants that register for
> itself, then it can build its own mpidr-vcpuid map if necessary.
> Ship it :-)
>
Thanks for the suggestion, Reiji. I'll send out a patch soon for this.

Regards,
Raghavendra
> Thanks,
> drew
>