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

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Message-ID: <d587af46-72cb-8fc7-8432-36473b67de47@redhat.com>
Date:   Thu, 26 Apr 2018 23:02:39 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     "Luis R . Rodriguez" <mcgrof@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>, Peter Jones <pjones@...hat.com>,
        Dave Olsthoorn <dave@...aar.me>,
        Will Deacon <will.deacon@....com>,
        Andy Lutomirski <luto@...nel.org>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        David Howells <dhowells@...hat.com>,
        Mimi Zohar <zohar@...ux.vnet.ibm.com>,
        Josh Triplett <josh@...htriplett.org>,
        Dmitry Torokhov <dmitry.torokhov@...il.com>,
        Martin Fuzzey <mfuzzey@...keon.com>,
        Kalle Valo <kvalo@...eaurora.org>,
        Arend Van Spriel <arend.vanspriel@...adcom.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Nicolas Broeking <nbroeking@...com>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Torsten Duwe <duwe@...e.de>, Kees Cook <keescook@...omium.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        linux-efi@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v4 1/5] efi: Export boot-services code and data as
 debugfs-blobs

Hi,

On 26-04-18 18:51, Ard Biesheuvel wrote:
> On 26 April 2018 at 14:06, Hans de Goede <hdegoede@...hat.com> 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@...uxfoundation.org>
>> Signed-off-by: Hans de Goede <hdegoede@...hat.com>
>> ---
>> 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