linux-kernel - Re: [PATCH V5 3/3] efi: Use efi_rts_wq to invoke EFI Runtime Services

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Date:   Tue, 5 Jun 2018 21:55:16 +0200
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     "Prakhya, Sai Praneeth" <sai.praneeth.prakhya@...el.com>
Cc:     linux-efi <linux-efi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Lee Chun-Yi <jlee@...e.com>, Borislav Petkov <bp@...en8.de>,
        "Luck, Tony" <tony.luck@...el.com>,
        Will Deacon <will.deacon@....com>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        Mark Rutland <mark.rutland@....com>,
        Bhupesh Sharma <bhsharma@...hat.com>,
        Naresh Bhat <naresh.bhat@...aro.org>,
        "Neri, Ricardo" <ricardo.neri@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Subject: Re: [PATCH V5 3/3] efi: Use efi_rts_wq to invoke EFI Runtime Services

On 5 June 2018 at 21:29, Prakhya, Sai Praneeth
<sai.praneeth.prakhya@...el.com> wrote:
>> > +       case RESET_SYSTEM:
>> > +               __efi_call_virt(reset_system, *(int *)arg1,
>> > +                               *(efi_status_t *)arg2,
>> > +                               *(unsigned long *)arg3,
>> > +                               (efi_char16_t *)arg4);
>> > +               break;
>>
>> I noticed that -unsurprisingly- reboot no longer works with these changes.
>>
>> I will fix up the patch, and revert the efi_reset_system() change, both here and
>> below.
>
> Could you please let me know what the bug is here? I am unable to see it right away :(
> I have tested reboot on qemu x86_64 by passing "reboot=efi" as command line arg and
> saw that reboot is working fine.
>

My arm64 hangs at reboot or power off, unless i revert the ResetSystem() part.

But given that it is both risky (relying on a kthread running a
workqueue in the shutdown path) and unnecessary (ResetSystem() is not
supposed to return, and is only called by the kernel when the whole
system has already been torn down), I think the main reason is simply
that there is no reason to add it.


>> > @@ -340,7 +441,8 @@ static void virt_efi_reset_system(int reset_type,
>> >                         "could not get exclusive access to the firmware\n");
>> >                 return;
>> >         }
>> > -       __efi_call_virt(reset_system, reset_type, status, data_size, data);
>> > +       efi_queue_work(RESET_SYSTEM, &reset_type, &status, &data_size, data,
>> > +                      NULL);
>> >         up(&efi_runtime_lock);
>> >  }
>
> Regards,
> Sai