linux-kernel - Re: [PATCH 4.4 00/37] 4.4.110-stable review

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Date:   Thu, 11 Jan 2018 12:46:43 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Pavel Tatashin <pasha.tatashin@...cle.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Hugh Dickins <hughd@...gle.com>, Thomas Voegtle <tv@...96.de>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Shuah Khan <shuahkh@....samsung.com>, patches@...nelci.org,
        Ben Hutchings <ben.hutchings@...ethink.co.uk>,
        lkft-triage@...ts.linaro.org, stable <stable@...r.kernel.org>,
        Steve Sistare <steven.sistare@...cle.com>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH 4.4 00/37] 4.4.110-stable review

On Thu, Jan 11, 2018 at 12:37 PM, Thomas Gleixner <tglx@...utronix.de> wrote:
>
> 67a9108ed431 ("x86/efi: Build our own page table structures")
>
> got rid of EFI depending on real_mode_header->trampoline_pgd

So I think it only got rid of by default - the codepath is still
there, the allocation is still there, it's just that it's not actually
used unless somebody does that "efi=old_mmap" thing.

Looking around, there's at least one quirk for the SGI UV1 system that
enables EFI_OLD_MMAP automatically. There might be others that I
missed, but I think that's it.

So it *can* trigger without "efi=old_mmap", but not on any normal machines.

And as Pavel points out, even when the bug is active, it's pretty hard
to actually trigger.

But yeah, there may be other EFI patches that I didn't notice that
changed things in other ways too.

               Linus