linux-kernel - Re: [PATCH] xen/pvhvm: add soft reset on kexec/kdump support

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Date:	Tue, 29 Sep 2015 13:39:47 +0200
From:	Vitaly Kuznetsov <vkuznets@...hat.com>
To:	Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	xen-devel@...ts.xenproject.org, x86@...nel.org,
	David Vrabel <david.vrabel@...rix.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] xen/pvhvm: add soft reset on kexec/kdump support

Boris Ostrovsky <boris.ostrovsky@...cle.com> writes:

> On 09/25/2015 03:35 PM, Konrad Rzeszutek Wilk wrote:
>> On Fri, Sep 25, 2015 at 03:19:57PM -0400, Boris Ostrovsky wrote:
>>> On 09/25/2015 03:01 PM, Konrad Rzeszutek Wilk wrote:
>>>> On Fri, Sep 25, 2015 at 01:17:40PM -0400, Boris Ostrovsky wrote:
>>>>> On 09/25/2015 12:07 PM, Vitaly Kuznetsov wrote:
>>>>>>> Also, I am not sure I see how this new op will be used in the
>>>>>>> hypervisor --- currently AFAICS it is only processed under
>>>>>>> is_hardware_domain(). Are there other patches that will support HVM
>>>>>>> guests?
>>>>>> Please see my Xen series:
>>>>>> http://lists.xenproject.org/archives/html/xen-devel/2015-09/msg00547.html
>>>>>> (last 'full' submission).
>>>>>>
>>>>>> All patches from my 'toolstack-assisted approach to PVHVM guest kexec'
>>>>>> are already merged to xen.git (first 10 are already in 'master' and the
>>>>>> last one is in 'staging').
>>>>>>
>>>>> OK, so I was looking at the right tree. Then I don't understand how
>>>>> SHUTDOWN_soft_reset would be reached for a non-privileged domain. The only
>>>>> path that I see is
>>>>>
>>>>>      domain_shutdown()
>>>>>      {
>>>>>          ...
>>>>>          if ( is_hardware_domain(d) )
>>>>>              hwdom_shutdown(reason);
>>>>>          ...
>>>>>      }
>>>>>
>>>>> Is there another path to handle this op?
>>>> Yes:
>>>>   e1bd9812966de9a16f30a58e7162b80bd6af361b libxc: support XEN_DOMCTL_soft_reset operation
>>>> and
>>>>   c57e6ebd8c3e490e353e68d96abec1dad01e72f5 (lib)xl: soft reset support
>>>>
>>>
>>> That's toolstack issuing hypercalls from dom0.
>>>
>>> I am asking about (non-privileged) guest itself calling SCHEDOP_shutdown.
>> The hypervisor ends up calling:
>> __domain_finalise_shutdown which sends an VIRQ_DOM_EXC to dom0 which
>> makes the toolstack do all of those operations.
>
> OK. But the I don't see anyone checking that 'reason' (or
> 'shutdown_code') is SHUTDOWN_soft_reset. In other words, the guest can
> do 'xen_reboot(23)' or 'xen_reboot(154)'. Or, it seems, even
> 'xen_reboot(SHUTDOWN_reboot)'? The only value it shouldn't be is
> SHUTDOWN_suspend.

Xen hypervisor doesn't analyzie the reason, it is being analyzed by the
toolstack (XEN_DOMCTL_getdomaininfo returns this info encoded in flags
with XEN_DOMINF_shutdownshift shift).

-- 
  Vitaly
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