linux-kernel - Re: [PATCH linux 0/8] xen: pvhvm: support bootup on secondary vCPUs

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Date:	Wed, 29 Jun 2016 11:16:55 +0200
From:	Vitaly Kuznetsov <vkuznets@...hat.com>
To:	David Vrabel <david.vrabel@...rix.com>
Cc:	<xen-devel@...ts.xenproject.org>, <linux-kernel@...r.kernel.org>,
	<x86@...nel.org>, Stefano Stabellini <sstabellini@...nel.org>,
	Boris Ostrovsky <boris.ostrovsky@...cle.com>,
	Juergen Gross <jgross@...e.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Ingo Molnar" <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
	Julien Grall <julien.grall@...rix.com>
Subject: Re: [PATCH linux 0/8] xen: pvhvm: support bootup on secondary vCPUs

David Vrabel <david.vrabel@...rix.com> writes:

> On 28/06/16 17:47, Vitaly Kuznetsov wrote:
>> It may happen that Xen's and Linux's ideas of vCPU id diverge. In
>> particular, when we crash on a secondary vCPU we may want to do kdump
>> and unlike plain kexec where we do migrate_to_reboot_cpu() we try booting
>> on the vCPU which crashed. This doesn't work very well for PVHVM guests as
>> we have a number of hypercalls where we pass vCPU id as a parameter. These
>> hypercalls either fail or do something unexpected. To solve the issue we
>> need to have a mapping between Linux's and Xen's vCPU ids.
>
> Could the soft-reboot hypercall (optionally) return on vcpu 0?
>

In theory, yes, I think we can re-arrange vCPUs inside the hypervisor so
Linux will get them in the natural order after soft reset.

-- 
  Vitaly