Re: [PATCH v4 1/5] efi: Export boot-services code and data as debugfs-blobs

[Hans de Goede]

Hi,

On 26-04-18 18:51, Ard Biesheuvel wrote:
> On 26 April 2018 at 14:06, Hans de Goede <hdegoede@xxxxxxxxxx> wrote:
> > Sometimes it is useful to be able to dump the efi boot-services code and
> > data. This commit adds these as debugfs-blobs to /sys/kernel/debug/efi,
> > but only if efi=debug is passed on the kernel-commandline as this requires
> > not freeing those memory-regions, which costs 20+ MB of RAM.
> >
> > Reviewed-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>
> > ---
> > Changes in v4:
> > -Add new EFI_BOOT_SERVICES flag and use it to determine if the boot-services
> >   memory segments are available (and thus if it makes sense to register the
> >   debugfs bits for them)
> >
> > Changes in v2:
> > -Do not call pr_err on debugfs call failures
> > ---
> >   arch/x86/platform/efi/efi.c    |  1 +
> >   arch/x86/platform/efi/quirks.c |  4 +++
> >   drivers/firmware/efi/efi.c     | 53 ++++++++++++++++++++++++++++++++++
> >   include/linux/efi.h            |  1 +
> >   4 files changed, 59 insertions(+)
> >
> > diff --git a/arch/x86/platform/efi/efi.c b/arch/x86/platform/efi/efi.c
> > index 9061babfbc83..568b7ee3d323 100644
> > --- a/arch/x86/platform/efi/efi.c
> > +++ b/arch/x86/platform/efi/efi.c
> > @@ -208,6 +208,7 @@ int __init efi_memblock_x86_reserve_range(void)
> >               efi.memmap.desc_version);
> >
> >          memblock_reserve(pmap, efi.memmap.nr_map * efi.memmap.desc_size);
> > +       set_bit(EFI_BOOT_SERVICES, &efi.flags);
>
> I think it would be better if the flag conveys whether boot services
> regions are being preserved, because they will always exist when
> EFI_BOOT is set.
> The name should then reflect that as well, e.g., EFI_PRESERVE_BS_REGIONS.

Ok, I will rename the flag to EFI_PRESERVE_BS_REGIONS for v5
(I'm going to wait a bit with sending out v5 to give others a change
 to comment on v4).

> >          return 0;
> >   }
> > diff --git a/arch/x86/platform/efi/quirks.c b/arch/x86/platform/efi/quirks.c
> > index 36c1f8b9f7e0..16bdb9e3b343 100644
> > --- a/arch/x86/platform/efi/quirks.c
> > +++ b/arch/x86/platform/efi/quirks.c
> > @@ -376,6 +376,10 @@ void __init efi_free_boot_services(void)
> >          int num_entries = 0;
> >          void *new, *new_md;
> >
> > +       /* Keep all regions for /sys/kernel/debug/efi */
> > +       if (efi_enabled(EFI_DBG))
> > +               return;
> > +
>
> Why is this only necessary when EFI_DBG is enabled? How are you
> ensuring that the firmware is still in memory when the subsequent
> patches start relying on that?

The 2nd patch in this series makes init/main.c call
efi_check_for_embedded_firmwares() before efi_free_boot_services(),
efi_check_for_embedded_firmwares() then walks the dmi_system_id-s
"registered" (its a static list) by drivers and if their is a dmi_match
searches for the firmware described by the dmi_system_id.driver_data
ptr. If a firmware gets found it gets memdup-ed, so that we do not
have to keep all of the boot-services code around.

Regards,

Hans