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Message-ID: <e4934a021c17dc8bfd8b2bdd8a4543e9ffe09e58.camel@infradead.org>
Subject: Re: [PATCH v2 09/12] KVM: selftests / xen: set
 KVM_XEN_VCPU_ATTR_TYPE_VCPU_ID
From:   David Woodhouse <dwmw2@infradead.org>
To:     paul@xen.org, kvm@vger.kernel.org, linux-kernel@vger.kernel.org
Cc:     Paul Durrant <pdurrant@amazon.com>,
        Sean Christopherson <seanjc@google.com>,
        Paolo Bonzini <pbonzini@redhat.com>
Date:   Mon, 18 Sep 2023 13:26:26 +0100
In-Reply-To: <c91c5ec9-a917-6d20-1401-c11e27d16f90@xen.org>
References: <20230918112148.28855-1-paul@xen.org>
         <20230918112148.28855-10-paul@xen.org>
         <74077fcadd5ddc9dba742987e1419fc13713cd7a.camel@infradead.org>
         <c91c5ec9-a917-6d20-1401-c11e27d16f90@xen.org>
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On Mon, 2023-09-18 at 13:18 +0100, Paul Durrant wrote:
> On 18/09/2023 12:59, David Woodhouse wrote:
> > On Mon, 2023-09-18 at 11:21 +0000, Paul Durrant wrote:
> > > From: Paul Durrant <pdurrant@amazon.com>
> > >=20
> > > If the capability (KVM_XEN_HVM_CONFIG_EVTCHN_SEND) is present then se=
t
> > > the guest's vCPU id to match the chosen vcpu_info offset.
> >=20
> > I think from KVM's point of view, the vcpu_id is still zero. As is the
> > vcpu_idx. What you're setting is the *Xen* vcpu_id.
>=20
> Ok. I'll clarify the terminology; and I'll need to set it before the=20
> shinfo as noted on another thread.
>=20
> >=20
> > I like that it's *different* to the vcpu_id; we should definitely be
> > testing that case.
>=20
> How so?
>=20

Well, imagine you'd not got the kernel's get_vcpu_info_cache() right,
and you accidentally used v->vcpu_id instead of v->arch.xen.vcpu_id. An
easy mistake to make, right?

If you had made that mistake (you didn't; I checked), and if those
numbers had happened to be equal in this test... then this test
wouldn't have shown it.


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