[U-Boot] [PATCH 1/1] efi_loader: re-enable GRUB workaround on 32bit ARM

[Tom Rini]

On Sun, Jul 28, 2019 at 10:13:24AM +0200, Heinrich Schuchardt wrote:
> On 7/27/19 11:58 AM, Alexander Graf wrote:
> >
> > On 27.07.19 10:02, Heinrich Schuchardt wrote:
> >> GRUB on ARM 32bit prior to version 2.04 lacks proper handling of caches.
> >> In U-Boot v2019.04 a workaround for this was inadvertently removed.
> >>
> >> The workaround is currently also needed for booting on systems with
> >> caches
> >> that cannot be managed via CP15 (e.g. with an i.MX6 CPU).
> >>
> >> Re-enable the workaround and make it customizable.
> >>
> >> Fixes: f69d63fae281 ("efi_loader: use efi_start_image() for bootefi")
> >> Signed-off-by: Heinrich Schuchardt <xypron.glpk at gmx.de>
> >> ---
> >>   lib/efi_loader/Kconfig        |  8 ++++++++
> >>   lib/efi_loader/efi_boottime.c | 28 +++++++++++++---------------
> >>   2 files changed, 21 insertions(+), 15 deletions(-)
> >>
> >> diff --git a/lib/efi_loader/Kconfig b/lib/efi_loader/Kconfig
> >> index a7f2c68fa9..c7027a9676 100644
> >> --- a/lib/efi_loader/Kconfig
> >> +++ b/lib/efi_loader/Kconfig
> >> @@ -107,4 +107,12 @@ config EFI_HAVE_RUNTIME_RESET
> >>       default y
> >>       depends on ARCH_BCM283X || FSL_LAYERSCAPE || PSCI_RESET ||
> >> SYSRESET_X86
> >>
> >> +config EFI_GRUB_ARM32_WORKAROUND
> >> +    bool "Workaround for GRUB on 32bit ARM"
> >> +    default y
> >> +    depends on ARM && !ARM64
> >> +    help
> >> +      GRUB prior to version 2.04 requires U-Boot to disable caches. This
> >> +      workaround currently is also needed on systems with caches that
> >> +      cannot be managed via CP15.
> >>   endif
> >> diff --git a/lib/efi_loader/efi_boottime.c
> >> b/lib/efi_loader/efi_boottime.c
> >> index 4f6e8d1679..f75ca1a67c 100644
> >> --- a/lib/efi_loader/efi_boottime.c
> >> +++ b/lib/efi_loader/efi_boottime.c
> >> @@ -39,14 +39,6 @@ LIST_HEAD(efi_register_notify_events);
> >>   /* Handle of the currently executing image */
> >>   static efi_handle_t current_image;
> >>
> >> -/*
> >> - * If we're running on nasty systems (32bit ARM booting into non-EFI
> >> Linux)
> >> - * we need to do trickery with caches. Since we don't want to break
> >> the EFI
> >> - * aware boot path, only apply hacks when loading exiting directly
> >> (breaking
> >> - * direct Linux EFI booting along the way - oh well).
> >> - */
> >> -static bool efi_is_direct_boot = true;
> >
> >
> > By removing the toggling, you now couple a U-Boot configuration variant
> > to a specific grub version. New grub versions will run Linux using the
> > EFI stub. So enabling CONFIG_EFI_GRUB_ARM32_WORKAROUND means only old
> > versions work, but new grub versions break.
> 
> No, the Wandboard boots fine with GRUB 2.04 and Linux 4.19.55. Do you
> have any negative test results?
> 
> >
> > We really should treat this like any other erratum and make it as
> > runtime detected as possible, so that we don't block people from making
> > forward progress towards a the "sane" boot path.
> 
> It is not possible to determine at runtime which assumptions a loaded
> EFI binary makes about the cache. Your original logic counting the
> number of StartImage() invocations cannot detect this. This is why I
> added a customizing option.
> 
> >
> > Btw, has there been any solution for the non-CP15 caches? They would
> > still be broken with this applied, as payloads can rely on CP15 caches
> > enabled (for unaligned accesses), but non-CP15 caches disabled, right?
> 
> No, this will need future work. With CONFIG_EFI_GRUB_ARM32_WORKAROUND=y
> all caches are disabled.
> 
> On i.MX6 CONFIG_SYS_L2CACHE_OFF=y selectively disables the non-CP15
> cache. So here CONFIG_EFI_GRUB_ARM32_WORKAROUND=n and
> CONFIG_SYS_L2CACHE_OFF=y result in compliance with the UEFI spec.

Where did all of this end up, in terms of what combinations of things do
/ don't work, on current master (or v2019.10-rc2) ?  Thanks all!

-- 
Tom
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