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

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Message-Id: <24F4CAC3-6596-4DCD-AC91-4BAF5F2B18B7@amacapital.net>
Date:   Sat, 2 Dec 2017 05:34:19 -0800
From:   Andy Lutomirski <luto@...capital.net>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Andy Lutomirski <luto@...nel.org>, 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 Dec 2, 2017, at 2:47 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
> 
>> 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. 

Hmm.  My second patch should make this go away, though.