linux-kernel - Re: [PATCH] arm64: xen: Implement EFI reset

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Message-ID: <c23a6d11-cde8-7690-9676-537b5f17b967@suse.com>
Date:   Thu, 6 Apr 2017 18:22:44 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Daniel Kiper <daniel.kiper@...cle.com>,
        Julien Grall <julien.grall@....com>
Cc:     Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        xen-devel@...ts.xen.org, sstabellini@...nel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] arm64: xen: Implement EFI reset_system callback

On 06/04/17 18:06, Daniel Kiper wrote:
> Hi Julien,
> 
> On Thu, Apr 06, 2017 at 04:39:13PM +0100, Julien Grall wrote:
>> Hi Daniel,
>>
>> On 06/04/17 16:20, Daniel Kiper wrote:
>>> On Thu, Apr 06, 2017 at 04:38:24PM +0200, Juergen Gross wrote:
>>>> On 06/04/17 16:27, Daniel Kiper wrote:
>>>>> On Thu, Apr 06, 2017 at 09:32:32AM +0100, Julien Grall wrote:
>>>>>> Hi Juergen,
>>>>>>
>>>>>> On 06/04/17 07:23, Juergen Gross wrote:
>>>>>>> On 05/04/17 21:49, Boris Ostrovsky wrote:
>>>>>>>> On 04/05/2017 02:14 PM, Julien Grall wrote:
>>>>>>>>> The x86 code has theoritically a similar issue, altought EFI does not
>>>>>>>>> seem to be the preferred method. I have left it unimplemented on x86 and
>>>>>>>>> CCed Linux Xen x86 maintainers to know their view here.
>>>>>>>>
>>>>>>>> (+Daniel)
>>>>>>>>
>>>>>>>> This could be a problem for x86 as well, at least theoretically.
>>>>>>>> xen_machine_power_off() may call pm_power_off(), which is efi.reset_system.
>>>>>>>>
>>>>>>>> So I think we should have a similar routine there.
>>>>>>>
>>>>>>> +1
>>>>>>>
>>>>>>> I don't see any problem with such a routine added, in contrast to
>>>>>>> potential "reboots" instead of power off without it.
>>>>>>>
>>>>>>> So I think this dummy xen_efi_reset_system() should be added to
>>>>>>> drivers/xen/efi.c instead.
>>>>>>
>>>>>> I will resend the patch during day with xen_efi_reset_system moved
>>>>>> to common code and implement the x86 counterpart (thought, I will
>>>>>> not be able to test it).
>>>>>
>>>>> I think that this is ARM specific issue. On x86 machine_restart() calls
>>>>> xen_restart(). Hence, everything works. So, I think that it should be
>>>>> fixed only for ARM. Anyway, please CC me when you send a patch.
>>>>
>>>> What about xen_machine_power_off() (as stated in Boris' mail)?
>>>
>>> Guys what do you think about that:
>>>
>>> --- a/drivers/firmware/efi/reboot.c
>>> +++ b/drivers/firmware/efi/reboot.c
>>> @@ -55,7 +55,7 @@ static void efi_power_off(void)
>>>
>>> static int __init efi_shutdown_init(void)
>>> {
>>> -       if (!efi_enabled(EFI_RUNTIME_SERVICES))
>>> +       if (!efi_enabled(EFI_RUNTIME_SERVICES) || efi_enabled(EFI_PARAVIRT))
>>>                return -ENODEV;
>>>
>>>        if (efi_poweroff_required())
>>>
>>>
>>> Julien, for ARM64 please take a look at arch/arm64/kernel/efi.c:efi_poweroff_required(void).
>>>
>>> I hope that tweaks for both files should solve our problem.
>>
>> This sounds good for power off (I haven't tried to power off DOM0
>> yet). But this will not solve the restart problem (see
>> machine_restart in arch/arm64/kernel/process.c) which call directly
>> efi_reboot.
> 
> Hmmm... It seems to me that efi.reset_system override with empty function
> in arch/arm/xen/efi.c is the best solution. So, I see three patches here.
> One for drivers/firmware/efi/reboot.c, one for arch/arm/xen/efi.c and one
> for arch/arm64/kernel/efi.c. Does it make sense?

I still think the empty function should be in drivers/xen/efi.c and we
should use it in arch/x86/xen/efi.c, too.


Juergen