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From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
To: Sasha Levin <sashal@kernel.org>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	stable <stable@vger.kernel.org>,
	Jeremy Linton <jeremy.linton@arm.com>,
	linux-efi <linux-efi@vger.kernel.org>
Subject: Re: [PATCH AUTOSEL 4.19 133/191] efi: honour memory reservations passed via a linux specific config table
Date: Sun, 10 Nov 2019 14:16:57 +0000
Message-ID: <CAKv+Gu_Pg-j6C0iRqa8wSr+=vk3rMQ=KHFykZGNGWMfcYfAjtg@mail.gmail.com> (raw)
In-Reply-To: <20191110132726.GN4787@sasha-vm>

On Sun, 10 Nov 2019 at 13:27, Sasha Levin <sashal@kernel.org> wrote:
>
> On Sun, Nov 10, 2019 at 08:33:47AM +0100, Ard Biesheuvel wrote:
> >On Sun, 10 Nov 2019 at 03:44, Sasha Levin <sashal@kernel.org> wrote:
> >>
> >> From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> >>
> >> [ Upstream commit 71e0940d52e107748b270213a01d3b1546657d74 ]
> >>
> >> In order to allow the OS to reserve memory persistently across a
> >> kexec, introduce a Linux-specific UEFI configuration table that
> >> points to the head of a linked list in memory, allowing each kernel
> >> to add list items describing memory regions that the next kernel
> >> should treat as reserved.
> >>
> >> This is useful, e.g., for GICv3 based ARM systems that cannot disable
> >> DMA access to the LPI tables, forcing them to reuse the same memory
> >> region again after a kexec reboot.
> >>
> >> Tested-by: Jeremy Linton <jeremy.linton@arm.com>
> >> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> >> Signed-off-by: Sasha Levin <sashal@kernel.org>
> >
> >NAK
> >
> >This doesn't belong in -stable, and I'd be interested in understanding
> >how this got autoselected, and how I can prevent this from happening
> >again in the future.
>
> It was selected because it's part of a fix for a real issue reported by
> users:
>

For my understanding, are you saying your AI is reading launchpad bug
reports etc? Because it is marked AUTOSEL.

> https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1806766
>

That pages mentions

"""
2 upstream patch series are required to fix this:
 https://<email address hidden>/msg10328.html
Which provides an EFI facility consumed by:
 https://lkml.org/lkml/2018/9/21/1066
There were also some follow-on fixes to deal with ARM-specific
problems associated with this usage:
 https://www.spinics.net/lists/arm-kernel/msg685751.html
"""

and without the other patches, we only add bugs and don't fix any.

> Besides ubuntu, it is also carried by:
>
> SUSE: https://www.suse.com/support/update/announcement/2019/suse-su-20191530-1/
> CentOS: https://koji.mbox.centos.org/koji/buildinfo?buildID=4558
>
> As a way to resolve the reported bug.
>

Backporting a feature/fix like this requires careful consideration of
the patches involved, and doing actual testing on hardware.

> Any reason this *shouldn't* be in stable?

Yes. By itself, it causes crashes at early boot and does not actually
solve the problem.

> I'm aware that there might be
> dependencies that are not obvious to me, but the solution here is to
> take those dependencies as well rather than ignore the process
> completely.
>

This is not a bugfix. kexec/kdump never worked correctly on the
hardware involved, and backporting a feature like that goes way beyond
what I am willing to accept for stable backports affecting the EFI
subsystem.

  reply index

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <20191110024013.29782-1-sashal@kernel.org>
2019-11-10  2:39 ` Sasha Levin
2019-11-10  7:33   ` Ard Biesheuvel
2019-11-10 13:27     ` Sasha Levin
2019-11-10 14:16       ` Ard Biesheuvel [this message]
2019-11-10 15:56         ` Sasha Levin
2019-11-10 16:26           ` Ard Biesheuvel
2019-11-10 18:08             ` Marc Zyngier
2019-11-10  2:39 ` [PATCH AUTOSEL 4.19 134/191] efi: Make efi_rts_work accessible to efi page fault handler Sasha Levin
2019-11-10  7:35   ` Ard Biesheuvel
2019-11-10  2:39 ` [PATCH AUTOSEL 4.19 135/191] efi/x86: Handle page faults occurring while running EFI runtime services Sasha Levin
2019-11-10  7:40   ` Ard Biesheuvel
2019-11-10  2:40 ` [PATCH AUTOSEL 4.19 191/191] x86/efi: fix a -Wtype-limits compilation warning Sasha Levin

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