EFI_STUB doesn't work if PREEMPT_RT

EFI_STUB doesn't work if PREEMPT_RT

[Alec Ari]

Hi,

I'm running Debian on a test system, CSM has been disabled. if I boot
the stock non-RT Debian kernel, I can use efibootmgr. When I try
booting the PREEMPT_RT package (linux-image-rt-amd64) or a custom
PREEMPT_RT kernel with the following config options enabled:

CONFIG_EFI=y
CONFIG_EFI_STUB=y
# CONFIG_EFI_MIXED is not set
# EFI (Extensible Firmware Interface) Support
CONFIG_EFI_VARS=y
CONFIG_EFI_ESRT=y
CONFIG_EFI_FAKE_MEMMAP=y
CONFIG_EFI_MAX_FAKE_MEM=8
CONFIG_EFI_RUNTIME_WRAPPERS=y
CONFIG_EFI_BOOTLOADER_CONTROL=y
# CONFIG_EFI_CAPSULE_LOADER is not set
# CONFIG_EFI_TEST is not set
CONFIG_EFI_PARTITION=y
CONFIG_FB_EFI=y
CONFIG_EFIVAR_FS=y
# CONFIG_EFI_PGT_DUMP is not set
CONFIG_FAT_FS=y
CONFIG_VFAT_FS=y
CONFIG_FAT_DEFAULT_CODEPAGE=437
CONFIG_FAT_DEFAULT_IOCHARSET="iso8859-1"
CONFIG_FAT_DEFAULT_UTF8=y

I get this message:

EFI variables are not supported on this system.

Mount and everything looks the same as it does in the non-RT kernel:

/dev/sda2 on /boot/efi type vfat
(rw,relatime,fmask=0077,dmask=0077,codepage=437,iocharset=iso8859-1,shortname=mixed,utf8,errors=remount-ro)

Adding `add_efi_memmap` to kernel params doesn't fix this either. When
using a non-PREEMPT_RT kernel, everything with EFI works.

Any idea? Is this a known issue with PREEMPT_RT?

Alec

Re: EFI_STUB doesn't work if PREEMPT_RT

[Alec Ari]

I should note, I'm using this PREEMPT_RT kernel:

linux-image-4.19.0-5-rt-amd64 (4.19.37-3)

When building the kernel myself, I used the linux-5.0.y-rt git branch:

https://git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git/log/?h=linux-5.0.y-rt

Alec

Re: EFI_STUB doesn't work if PREEMPT_RT

[Alec Ari]

One more thing, I think this is all related to this message when
booting the Debian PREEMPT_RT kernel:

[    0.556708] efi: EFI_MEMMAP is not enabled.

When compiling the EFI options into kernel (Y) instead of a module (M)
the message disappears but the problem remains. Switching between the
signed and unsigned preempt_rt kernel packages have no effect.

Sorry for the noise.

Alec

Re: EFI_STUB doesn't work if PREEMPT_RT

[Scott Wood]

On Mon, 2019-06-10 at 15:46 -0500, Alec Ari wrote:
> Hi,
> 
> I'm running Debian on a test system, CSM has been disabled. if I boot
> the stock non-RT Debian kernel, I can use efibootmgr. When I try
> booting the PREEMPT_RT package (linux-image-rt-amd64) or a custom
> PREEMPT_RT kernel with the following config options enabled:

It's disabled by default on PREEMPT_RT due to latency concerns.  You can
override it with "efi=runtime" on the kernel command line.

-Scott

Re: EFI_STUB doesn't work if PREEMPT_RT

[Alec Ari]

Hi,

Thank you, Scott! That explains everything, appreciate it! I wanted to
do latency testing with PREEMPT_RT under EFI and couldn't figure out
what I was doing wrong.

Alec

Re: EFI_STUB doesn't work if PREEMPT_RT

[Alec Ari]

EFI Stub is working now, thanks again. Latency isn't affected by EFI
on this particular board (ASUS TUF B450M-Plus Gaming) with Ryzen 2200G
and BIOS version 1003 (dated 2019/04/30 -- Latest as of this writing.)

Alec

On Mon, Jun 10, 2019 at 9:47 PM Alec Ari <neotheuser@gmail.com> wrote:
>
> Hi,
>
> Thank you, Scott! That explains everything, appreciate it! I wanted to
> do latency testing with PREEMPT_RT under EFI and couldn't figure out
> what I was doing wrong.
>
> Alec

Re: EFI_STUB doesn't work if PREEMPT_RT

[Sebastian Andrzej Siewior]

On 2019-06-12 12:01:46 [-0500], Alec Ari wrote:
> EFI Stub is working now, thanks again. Latency isn't affected by EFI
> on this particular board (ASUS TUF B450M-Plus Gaming) with Ryzen 2200G
> and BIOS version 1003 (dated 2019/04/30 -- Latest as of this writing.)

Did you try to modify EFI variables?

> Alec

Sebastian

Re: EFI_STUB doesn't work if PREEMPT_RT

[Alec Ari]

Yes,

All is fine with efi=runtime.

Alec

On Fri, Jun 14, 2019 at 2:36 PM Sebastian Andrzej Siewior
<bigeasy@linutronix.de> wrote:
>
> On 2019-06-12 12:01:46 [-0500], Alec Ari wrote:
> > EFI Stub is working now, thanks again. Latency isn't affected by EFI
> > on this particular board (ASUS TUF B450M-Plus Gaming) with Ryzen 2200G
> > and BIOS version 1003 (dated 2019/04/30 -- Latest as of this writing.)
>
> Did you try to modify EFI variables?
>
> > Alec
>
> Sebastian