linux-kernel - Re: efi boot failures due to PTI with 32 bit builds and Intel CPUs

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Date:   Thu, 30 Aug 2018 20:46:39 +0200
From:   Joerg Roedel <jroedel@...e.de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Guenter Roeck <linux@...ck-us.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Michal Hocko <mhocko@...e.com>,
        Andi Kleen <ak@...ux.intel.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Pavel Machek <pavel@....cz>
Subject: Re: efi boot failures due to PTI with 32 bit builds and Intel CPUs

On Thu, Aug 30, 2018 at 11:21:49AM -0700, Linus Torvalds wrote:
> On Thu, Aug 30, 2018 at 11:08 AM Joerg Roedel <jroedel@...e.de> wrote:
> >
> > Without a mapped GDT the #PF and #DF handlers also can't be started, so
> > the machine triple-faults. Below diff fixes it for me, I'll send a
> > proper patch tomorrow.
> 
> Hmm. Is there any reason why this code doesn't just use
> 
>         load_fixmap_gdt(0);

No idea, probably the function didn't exist when the code was written?
I can change that when writing the patch.

> and shouldn't it do it after loading the new %cr3?

That seems more robust, yes. No sure if the old %cr3
(initial_page_table) has the fixmap gdt mapped at all.


	Joerg