linux-kernel - Re: [PATCH] efi: Allow to enable EFI runtime services with PREEMPT

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Date:   Thu, 31 Mar 2022 16:25:40 +0200
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Cc:     linux-kernel@...r.kernel.org, Peter Jones <pjones@...hat.com>,
        Alexander Larsson <alexl@...hat.com>,
        Al Stone <ahs3@...hat.com>, linux-efi@...r.kernel.org,
        Ard Biesheuvel <ardb@...nel.org>,
        Andrew Halaney <ahalaney@...hat.com>,
        linux-rt-users@...r.kernel.org, Brian Masney <bmasney@...hat.com>,
        Robbie Harwood <rharwood@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] efi: Allow to enable EFI runtime services with PREEMPT_RT

Hello Sebastian,

On 3/31/22 16:13, Sebastian Andrzej Siewior wrote:
> On 2022-03-31 16:10:38 [+0200], Javier Martinez Canillas wrote:
>> Commit d9f283ae71af ("efi: Disable runtime services on RT") disabled EFI
>> runtime services when the CONFIG_PREEMPT_RT option is enabled.
>>
>> The rationale for the change is that some EFI calls could take too much
>> time, leading to large latencies which are an issue for RT kernels.
>>
>> But a side effect of that commit is that now is not possible anymore to
>> enable the EFI runtime services by default when CONFIG_PREEMPT_RT is set
>> to y, even for platforms that could guarantee bounded time for EFI calls.
>>
>> Instead, let's add a new EFI_DISABLE_RUNTIME boolean Kconfig option, that
>> would be set to n by default but to y if CONFIG_PREEMPT_RT is enabled.
>>
>> That way, the current behaviour is preserved but gives users a mechanism
>> to enable the EFI runtimes services in their kernels if that is required.
> 
> Is the command line switch
> 	efi=runtime
> 
> not working?
>

Yes, it is but the motivation is to be able to have EFI runtime services
by default without the need for any kernel command line parameter.

In the same vein, I could ask if efi=noruntime wasn't enough instead of
commit ("efi: Disable runtime services on RT").

-- 
Best regards,

Javier Martinez Canillas
Linux Engineering
Red Hat