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

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Message-ID: <87si62pjnd.fsf@vitty.brq.redhat.com>
Date:	Fri, 25 Sep 2015 18:07:34 +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 09:59 AM, Konrad Rzeszutek Wilk wrote:
>> On Fri, Sep 25, 2015 at 11:59:52AM +0200, Vitaly Kuznetsov wrote:
>>> Currently there is a number of issues preventing PVHVM Xen guests from
>>> doing successful kexec/kdump:
>>> - Bound event channels.
>>> - Registered vcpu_info.
>>> - PIRQ/emuirq mappings.
>>> - shared_info frame after XENMAPSPACE_shared_info operation.
>>> - Active grant mappings.
>>> Basically, newly booted kernel stumbles upon already set up Xen interfaces
>>> and there is no way to reestablish them. In Xen-4.7 a new feature called
>>> 'soft reset' is coming. A guest performing kexec/kdump operation is
>>> supposed to call SCHEDOP_shutdown hypercall with SHUTDOWN_soft_reset reason
>>> before jumping to new kernel. Hypervisor (with some help from toolstack)
>>> will do full domain cleanup (but keeping its memory and vCPU contexts
>>> intact) returning the guest to the state it had when it was first booted
>>> and thus allowing it to start over.
>>>
>>> Doing SHUTDOWN_soft_reset on Xen hypervisors which don't support it is
>>> probably OK as by default all unknown shutdown reasons cause domain destroy
>>> with a message in toolstack log:
>>> 'Unknown shutdown reason code 5. Destroying domain.'
>>> which gives a clue to what the problem is and eliminates false
>>> expectations.
>>>
>>> Signed-off-by: Vitaly Kuznetsov <vkuznets@...hat.com>
>> Reviewed-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
>>
>> with s/pvhvm/hvm/
>>
>> to match with the rest of the file.
>>
>> Thanks.
>>>   +#ifdef CONFIG_KEXEC_CORE
>>> +static void xen_pvhvm_kexec_shutdown(void)
>>> +{
>>> +	native_machine_shutdown();
>>> +	if (kexec_in_progress)
>>> +		xen_reboot(SHUTDOWN_soft_reset);
>>> +}
>
> This routine is not kexec-specific so "kexec_" should be dropped from
> the name.

Ok,

>
> 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').

-- 
  Vitaly
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