linux-kernel - Re: [PATCHv7 5/4] x86/boot/compressed/64: Support switching from 5- to 4-level paging

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Message-ID: <20180129153945.sme6f2zx3fpj24qy@node.shutemov.name>
Date:   Mon, 29 Jan 2018 18:39:45 +0300
From:   "Kirill A. Shutemov" <kirill@...temov.name>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     Ingo Molnar <mingo@...hat.com>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andy Lutomirski <luto@...capital.net>,
        Cyrill Gorcunov <gorcunov@...nvz.org>,
        Borislav Petkov <bp@...e.de>, Andi Kleen <ak@...ux.intel.com>,
        Matthew Wilcox <willy@...radead.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCHv7 5/4] x86/boot/compressed/64: Support switching from 5-
 to 4-level paging

On Mon, Jan 29, 2018 at 06:07:58PM +0300, Kirill A. Shutemov wrote:
> +	/*
> +	 * We are in 5-level paging mode, but we want to switch to 4-level.
> +	 * Let's take the first entry in the top-level page table as our new CR3.
> +	 */
> +	movl	%cr3, %eax
> +	movl	(%eax), %eax
> +	movl	%eax, %cr3

Aghh.. Please ignore this.

It would fail if CR3 points above 4G.

-- 
 Kirill A. Shutemov