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Subject: Re: [Xen-devel] [PATCH linux 2/8] xen: introduce xen_vcpu_id mapping
To: Vitaly Kuznetsov <vkuznets@redhat.com>, <xen-devel@lists.xenproject.org>
References: <1467132449-1030-1-git-send-email-vkuznets@redhat.com>
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CC: Juergen Gross <jgross@suse.com>,
        Stefano Stabellini <sstabellini@kernel.org>, <x86@kernel.org>,
        <linux-kernel@vger.kernel.org>, Julien Grall <julien.grall@citrix.com>,
        Ingo Molnar <mingo@redhat.com>,
        "David Vrabel" <david.vrabel@citrix.com>,
        "H. Peter Anvin" <hpa@zytor.com>,
        "Boris Ostrovsky" <boris.ostrovsky@oracle.com>,
        Thomas Gleixner <tglx@linutronix.de>
From: Andrew Cooper <andrew.cooper3@citrix.com>
Message-ID: <c16250fe-28a4-20d6-2c47-6c2d3cae85ff@citrix.com>
Date: Tue, 28 Jun 2016 18:28:31 +0100
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On 28/06/16 17:47, Vitaly Kuznetsov wrote:
> @@ -1808,6 +1822,8 @@ static int xen_hvm_cpu_notify(struct notifier_block *self, unsigned long action,
>  	int cpu = (long)hcpu;
>  	switch (action) {
>  	case CPU_UP_PREPARE:
> +		/* vLAPIC_ID == Xen's vCPU_ID * 2 for HVM guests */
> +		per_cpu(xen_vcpu_id, cpu) = cpu_physical_id(cpu) / 2;

Please do not assume or propagate this brokenness.  It is incorrect in
the general case, and I will be fixing in the hypervisor in due course.

Always read the APIC_ID from the LAPIC, per regular hardware.

~Andrew