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Date:   Mon, 13 Sep 2021 09:35:12 +0200
From:   Andrew Jones <drjones@redhat.com>
To:     Reiji Watanabe <reijiw@google.com>
Cc:     Raghavendra Rao Ananta <rananta@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
Subject: Re: [PATCH v4 09/18] KVM: arm64: selftests: Add guest support to get
 the vcpuid
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 <20210909013818.1191270-10-rananta@google.com>
 <CAAeT=Fw0Z1USVpdi2iRMRq0ktTP4+VFzfy31FWV36VPOCTq6_w@mail.gmail.com>
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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,
drew