linux-kernel - Re: [PATCH v2] efi: Allow to enable EFI runtime services by default on RT

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Date:   Fri, 1 Apr 2022 10:34:03 +0200
From:   Ard Biesheuvel <ardb@...nel.org>
To:     Javier Martinez Canillas <javierm@...hat.com>
Cc:     Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
        "Ahmed S. Darwish" <a.darwish@...utronix.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-efi <linux-efi@...r.kernel.org>,
        Brian Masney <bmasney@...hat.com>, Al Stone <ahs3@...hat.com>,
        Peter Robinson <pbrobinson@...il.com>,
        Robbie Harwood <rharwood@...hat.com>,
        Peter Jones <pjones@...hat.com>,
        Alexander Larsson <alexl@...hat.com>,
        Andrew Halaney <ahalaney@...hat.com>,
        linux-rt-users@...r.kernel.org,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH v2] efi: Allow to enable EFI runtime services by default
 on RT

On Fri, 1 Apr 2022 at 10:33, Javier Martinez Canillas
<javierm@...hat.com> wrote:
>
> Hello Sebastian,
>
> On 4/1/22 09:42, Sebastian Andrzej Siewior wrote:
> > On 2022-04-01 00:19:57 [+0200], Javier Martinez Canillas wrote:
> >>> In case of (CONFIG_PREEMPT_RT=y && CONFIG_EFI_DISABLE_RUNTIME=n),
> >>> shouldn't we add a small message in the kernel log warning that EFI
> >>> runtime services are enabled for the RT kernel?
> >>>
> >>> In almost all HW, except custom ones with "verified" firmware, such a
> >>> warning would be useful... This is especially true since in the embedded
> >>
> >> I considered that as well but was not sure about what that message should be.
> >
> > This makes sense and we had this in the past but dropped it for some
> > reason.
> >
>
> Ok, something like the following maybe? If you agree, I'll squash in v3:
>
> diff --git a/drivers/firmware/efi/efi.c b/drivers/firmware/efi/efi.c
> index ff57db8f8d05..08d329a5179b 100644
> --- a/drivers/firmware/efi/efi.c
> +++ b/drivers/firmware/efi/efi.c
> @@ -362,6 +362,8 @@ static int __init efisubsys_init(void)
>
>         if (!efi_enabled(EFI_RUNTIME_SERVICES))
>                 efi.runtime_supported_mask = 0;
> +       else if (IS_ENABLED(CONFIG_PREEMPT_RT))
> +               pr_warn("EFI runtime services can lead to high latencies on Real-Time kernels\n");
>
>         if (!efi_enabled(EFI_BOOT))
>                 return 0;
>


I don't think we need another warning.

The kernel log already tells you whether or not EFI runtime services
are enabled.