linux-kernel - Re: [PATCH 1/2] Undo the split of setup_cpu_entry

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Message-ID: <alpine.DEB.2.20.1712021146320.2199@nanos>
Date:   Sat, 2 Dec 2017 11:47:15 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Andy Lutomirski <luto@...nel.org>
cc:     X86 ML <x86@...nel.org>, Borislav Petkov <bpetkov@...e.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Brian Gerst <brgerst@...il.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH 1/2] Undo the split of setup_cpu_entry_area

On Sat, 2 Dec 2017, Thomas Gleixner wrote:

> On Fri, 1 Dec 2017, Andy Lutomirski wrote:
> 
> > This is obviously a hack.  Either the patch should be adjusted back to
> > the version I sent or trap_init should forcibly initialize all PMDs
> > by something like __set_fixmap(..., __mkpte(0)); or however it's spelled.
> 
> I split it because the whole thing crashed when I kept the loop you had
> because it tried to allocate stuff. Had no time to figure out why, so I
> went the lazy way of making it "work".

[    0.000000]  dump_stack+0x85/0xc5
[    0.000000]  warn_alloc+0x114/0x1c0
[    0.000000]  __alloc_pages_slowpath+0x1089/0x10d0
[    0.000000]  __alloc_pages_nodemask+0x2e8/0x370
[    0.000000]  __get_free_pages+0x10/0x40
[    0.000000]  kpti_shadow_pagetable_walk+0x2b2/0x3e0
[    0.000000]  kpti_add_user_map+0xfe/0x330
[    0.000000]  kpti_add_mapping_cpu_entry+0x5a/0x100
[    0.000000]  trap_init+0x2c/0x7b
[    0.000000]  start_kernel+0x24c/0x497
[    0.000000]  secondary_startup_64+0xa5/0xb0

Cute, isn't it? And then further down the line it triplefaults of course.