linux-kernel - Re: Random crashes with i386 and efi boots

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Message-ID: <20180911174158.7qu6f4vfnfzqqrcf@suse.de>
Date:   Tue, 11 Sep 2018 19:41:58 +0200
From:   Joerg Roedel <jroedel@...e.de>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Guenter Roeck <linux@...ck-us.net>, linux-kernel@...r.kernel.org,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Michal Hocko <mhocko@...e.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Pavel Machek <pavel@....cz>, linux-efi@...r.kernel.org,
        x86@...nel.org
Subject: Re: Random crashes with i386 and efi boots

On Tue, Sep 11, 2018 at 09:36:51AM -0700, Andy Lutomirski wrote:
> >    save_pgd = efi_call_phys_prolog();
> >    local_irq_save(flags);
> >    status = efi_call_phys(...);
> >        local_irq_restore(flags);
> > 
> >        efi_call_phys_epilog(save_pgd);
> > 
> > So, yes, interrupts are very much enabled.
> 
> Does fixing that solve the problem?  It seems more robust.

The problem is still that in efi_call_phys_prolog() we load the gdt with
its physical address, and when we reload the %cr3 in _epilog from
initial_page_table to swapper_pg_dir again the gdt is no longer mapped.
Blocking interrupts is more robust, but we can't block NMIs that way
that would also trigger the issue, no?

So I am in favor of changing the order in efi_call_phys_epilog() too.

Regards,

	Joerg