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

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Date:   Thu, 6 Apr 2017 16:55:11 +0100
From:   Mark Rutland <mark.rutland@....com>
To:     Julien Grall <julien.grall@....com>
Cc:     Daniel Kiper <daniel.kiper@...cle.com>,
        Juergen Gross <jgross@...e.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>,
        sstabellini@...nel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, xen-devel@...ts.xen.org,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        linux-efi@...r.kernel.org
Subject: Re: [PATCH] arm64: xen: Implement EFI reset_system callback

[Adding the EFI maintainers]

Tl;DR: Xen's EFI wrappery doesn't implement reset_system, so when
invoked on arm64 we get a NULL dereference.

On Thu, Apr 06, 2017 at 04:39:13PM +0100, Julien Grall wrote:
> 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).

Please, let's keep the Xen knowledge constrained to the Xen EFI wrapper,
rather than spreading it further.

IMO, given reset_system is a *mandatory* function, the Xen wrapper
should provide an implementation.

I don't see why you can't implement a wrapper that calls the usual Xen
poweroff/reset functions.

Thanks,
Mark.