linux-kernel - Re: [GIT PULL] x86 fixes

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Date:   Sat, 16 Dec 2017 19:25:19 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Borislav Petkov <bp@...en8.de>
Subject: Re: [GIT PULL] x86 fixes

On Fri, Dec 15, 2017 at 8:07 AM, Ingo Molnar <mingo@...nel.org> wrote:
>
> * Andy Lutomirski <luto@...nel.org> wrote:
>
>> On Fri, Dec 15, 2017 at 7:43 AM, Ingo Molnar <mingo@...nel.org> wrote:
>> > Linus,
>>
>> >
>> >  - two 5-level paging related fixes
>>
>> Which reminds me: can you grab this one, too?
>>
>> https://lkml.kernel.org/r/24c898b4f44fdf8c22d93703850fb384ef87cfdc.1513035461.git.luto@kernel.org
>
> Yeah, done - it's now in x86/urgent as:
>
>   c739f930be1d: x86/espfix/64: Fix espfix double-fault handling on 5-level systems
>
> Will push it out soon. Linus will get it with the next x86/urgent batch, as
> there's no production 5-level paging CPUs out there yet, right?
>
> I'm also picking up your pending PTI fixes/updates over the weekend, but I spent
> today mostly to make sure that the system call trampoline bits and its
> dependencies were robust in practice.
>
> Could you please have a good look at that tree:
>
>    git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git tmp.tmp
>
> This includes the preparatory merges and cherry-picks, and some other low risk
> preparatory bits related to PTI.
>
> Is this tree looking good to you standalone?

I think this stuff is looking okay, although I'm a bit mystified by
the whole merge base thing.  But if the backporters and Linus like it,
then whatever.

I few things I noticed in the PTI tree:

"x86/mm/pti: Map ESPFIX into user space" has a leftover pr_err().
Sorry, my bad, I've spent *way* too long looking at this crap to
retain my sanity.  Also, if you're feeling like being super tidy, the
init/main.c change in their could be folded in to whatever patch adds
pti_init() in the first place, but it doesn't really matter.

"x86/pti: Map the vsyscall page if needed" has a change to
pgtable_64.h that could be folded into an earlier patch.  This is
probably my fault for applying Dave Hansen's cleanup request to the
wrong patch.

"x86/mm/64: Make a full PGD-entry size hole in the memory map" would
benefit from a mention of "5-level" somewhere in the subject or
changelog.

In "x86/fixmap: Add debugstore entries to cpu_entry_area", I think the
function "set_percpu_fixmap_ptes" is misnamed.  It should be something
like "allocate_percpu_fixmap_ptes", perhaps, and it should either warn
or do nothing if the PTE is already present, I think.  As it stands,
it's a wee bit dangerous.

X86_BUG_CPU_SECURE_MODE_PTI should be added to DISABLED_FEATURES or
DISABLED_BUGS or whatever if it's not configured in, which will reduce
bloat.  Borislav, that's kind of up your alley, since I don't think
the appropriate mask even exists right now.

Anyway, I stuck a few minor fixups here:

https://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git/log/?h=x86/pti