linux-kernel - Re: [tip:x86/boot] x86/boot/compressed/64: Handle 5-level paging boot if kernel is above 4G

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Date:   Tue, 13 Feb 2018 13:00:05 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     Ingo Molnar <mingo@...nel.org>
Cc:     Andrei Vagin <avagin@...tuozzo.com>,
        tip-bot for Jacob Shin <tipbot@...or.com>,
        kirill.shutemov@...ux.intel.com, linux-tip-commits@...r.kernel.org,
        tglx@...utronix.de, willy@...radead.org, gorcunov@...nvz.org,
        bp@...e.de, peterz@...radead.org, torvalds@...ux-foundation.org,
        hpa@...or.com, linux-kernel@...r.kernel.org, luto@...capital.net
Subject: Re: [tip:x86/boot] x86/boot/compressed/64: Handle 5-level paging
 boot if kernel is above 4G

On Tue, Feb 13, 2018 at 10:43:56AM +0100, Ingo Molnar wrote:
> 
> * Kirill A. Shutemov <kirill@...temov.name> wrote:
> 
> > On Tue, Feb 13, 2018 at 12:41:22AM -0800, Andrei Vagin wrote:
> > > On Tue, Feb 13, 2018 at 11:08:16AM +0300, Kirill A. Shutemov wrote:
> > > > On Mon, Feb 12, 2018 at 10:51:56PM -0800, Andrei Vagin wrote:
> > > > > Hi Kirill,
> > > > > 
> > > > > Something is wrong in this patch.
> > 
> > Could you please check if this makes a difference?
> > 
> > diff --git a/arch/x86/boot/compressed/head_64.S b/arch/x86/boot/compressed/head_64.S
> > index 70b30f2bc9e0..99a0e7993252 100644
> > --- a/arch/x86/boot/compressed/head_64.S
> > +++ b/arch/x86/boot/compressed/head_64.S
> > @@ -332,7 +332,7 @@ ENTRY(startup_64)
> >  
> >  	/* Make sure we have GDT with 32-bit code segment */
> >  	leaq	gdt(%rip), %rax
> > -	movl	%eax, gdt64+2(%rip)
> > +	movq	%rax, gdt64+2(%rip)
> >  	lgdt	gdt64(%rip)
> 
> There's another suspicious looking pattern as well:
> 
>         leaq    startup_32(%rip), %rax
>         movl    %eax, BP_code32_start(%rsi)
> ...
>         movl    BP_code32_start(%esi), %eax
>         leaq    startup_64(%rax), %rax
> ...

code32_start is 4-byte field as described in the boot protocol, so the
truncation is intentional I think.

-- 
 Kirill A. Shutemov