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

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Date:	Wed, 29 Jun 2016 13:36:47 +0100
From:	David Vrabel <david.vrabel@...rix.com>
To:	Vitaly Kuznetsov <vkuznets@...hat.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

On 29/06/16 10:16, Vitaly Kuznetsov wrote:
> 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.

The series is straight forwards and the concept of the guest having to
map its idea of CPU to VCPU is fine, so unless you think a hypervisor
based solution is better we can take this series once it's fixed up.

David