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Re: [qemu-s390x] [PATCH v1] s390x: refactor reset/reipl handling

From: David Hildenbrand
Subject: Re: [qemu-s390x] [PATCH v1] s390x: refactor reset/reipl handling
Date: Thu, 21 Jun 2018 18:08:47 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.8.0

On 21.06.2018 18:06, Christian Borntraeger wrote:
> On 06/21/2018 06:04 PM, Cornelia Huck wrote:
>> On Thu, 21 Jun 2018 17:49:56 +0200
>> Christian Borntraeger <address@hidden> wrote:
>>> On 04/24/2018 12:18 PM, David Hildenbrand wrote:
>>>> Calling pause_all_vcpus()/resume_all_vcpus() from a VCPU thread might
>>>> not be the best idea. As pause_all_vcpus() temporarily drops the qemu
>>>> mutex, two parallel calls to pause_all_vcpus() can be active at a time,
>>>> resulting in a deadlock. (either by two VCPUs or by the main thread and a
>>>> VCPU)
>>>> Let's handle it via the main loop instead, as suggested by Paolo. If we
>>>> would have two parallel reset requests by two different VCPUs at the
>>>> same time, the last one would win.
>>>> We use the existing ipl device to handle it. The nice side effect is
>>>> that we can get rid of reipl_requested.
>>>> This change implies that all reset handling now goes via the common
>>>> path, so "no-reboot" handling is now active for all kinds of reboots.  
>>> Ok, this breaks the s390 IPL process when -no-reboot  is specified.
>>> The bios does a diagnose 308 subcode 1 to jump to the final image while
>>> at the same time resetting all devices. This is now blocked with -no-reboot
>>> (although it is actually the boot)
>>> I have noticed that with virt-install on iso images since virt-install
>>> specifies -no-reboot.
>>> Something like this seems to help but it is not a nice solution.
>> It's a bit ugly, but allows us to accommodate the different semantics
>> for the different diag subcodes... the -no-reboot parameter is only
>> supposed to suppress normal guest reboot requests, right?
> At least thats how it worked until 2.12. Without this we have no 
> kdump/kexec/ipl
> as soon as somebody uses -no-reboot.
Paolo even said that consistent -no-reboot handling would be one of the
benefits :)

> Shall I respin my patch as proper patch?

Yes, sure.



David / dhildenb

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