linux-kernel - Re: [Patch v3 0/4] Protect against concurrent calls into UV BIOS

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Date:   Thu, 14 Feb 2019 15:08:39 -0600
From:   Russ Anderson <rja@....com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Cc:     Hedi Berriche <hedi.berriche@....com>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Borislav Petkov <bp@...en8.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Bhupesh Sharma <bhsharma@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        linux-efi <linux-efi@...r.kernel.org>,
        the arch/x86 maintainers <x86@...nel.org>,
        Mike Travis <mike.travis@....com>,
        Dimitri Sivanich <sivanich@....com>,
        Steve Wahl <steve.wahl@....com>,
        stable <stable@...r.kernel.org>
Subject: Re: [Patch v3 0/4] Protect against concurrent calls into UV BIOS

On Thu, Feb 14, 2019 at 09:17:37AM +0100, Ard Biesheuvel wrote:
> On Wed, 13 Feb 2019 at 20:34, Hedi Berriche <hedi.berriche@....com> wrote:
> >
> > - Changes since v2
> >   Addressed comments from Ard Biesheuvel:
> >  * expose efi_runtime_lock to UV platform only instead of globally
> >  * remove unnecessary #ifdef CONFIG_EFI from bios_uv.c
> >
> > - Changes since v1:
> >   Addressed comments from Bhupesh Sharma, Thomas Gleixner, and Ard Biesheuvel:
> >  * made __uv_bios_call() static
> >  * moved the efi_enabled() cleanup to its own patchlet
> >  * explained the reason for renaming the efi_runtime_lock semaphore
> >  * dropped the reviewed-bys as they should be given on the mailing list
> >  * Cc'ng stable@...r.kernel.org given the nature of the problem addressed by the patches
> >
> 
> Hi Hedi,
> 
> The patches look good to me now.
> 
> For the series,
> 
> Reviewed-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
> 
> However, I don't think all the patches should go to -stable. Only 4/4
> fixes an actual bug, and the remaining patches don't look like they
> are prerequisites for that change.
> 
> Also, if your colleagues reviewed your patches, now would be the time
> to ask them to give their Reviewed-by as well.

Reviewed-by: Russ Anderson <rja@....com>

Thanks.

> -- 
> Ard.
> 
> 
> 
> > ---
> >
> > Calls into UV BIOS were not being serialised which is wrong as it violates EFI
> > runtime rules, and bad as it does result in all sorts of potentially hard to
> > track down hangs and panics when efi_scratch.prev_mm gets clobbered whenever
> > efi_switch_mm() gets called concurrently from two different CPUs.
> >
> > Patch #1 removes an unnecessary #ifdef CONFIG_EFI guard from bios_uv.c.
> >
> > Patch #2 removes uv_bios_call_reentrant() because it's dead code.
> >
> > Patch #3 is a cleanup that drops test_bit() in favour of the ad hoc efi_enabled().
> >
> > Patch #4 makes uv_bios_call() variants use the efi_runtime_lock semaphore to
> > protect against concurrency.
> >
> > Cc: Russ Anderson <rja@....com>
> > Cc: Mike Travis <mike.travis@....com>
> > Cc: Dimitri Sivanich <sivanich@....com>
> > Cc: Steve Wahl <steve.wahl@....com>
> > Cc: stable@...r.kernel.org # v4.9+
> >
> > Hedi Berriche (4):
> >   x86/platform/UV: remove unnecessary #ifdef CONFIG_EFI
> >   x86/platform/UV: kill uv_bios_call_reentrant() as it has no callers
> >   x86/platform/UV: use efi_enabled() instead of test_bit()
> >   x86/platform/UV: use efi_runtime_lock to serialise BIOS calls
> >
> >  arch/x86/include/asm/uv/bios.h          | 13 ++++-----
> >  arch/x86/platform/uv/bios_uv.c          | 35 ++++++++++++++-----------
> >  drivers/firmware/efi/runtime-wrappers.c |  7 +++++
> >  3 files changed, 34 insertions(+), 21 deletions(-)
> >
> > --
> > 2.20.1
> >

-- 
Russ Anderson,  SuperDome Flex Linux Kernel Group Manager
HPE - Hewlett Packard Enterprise (formerly SGI)  rja@....com