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Date: Mon, 29 Jan 2018 03:59:27 -0800
From: Matthew Wilcox <willy@infradead.org>
To: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc: Ingo Molnar <mingo@redhat.com>, x86@kernel.org,
        Thomas Gleixner <tglx@linutronix.de>, "H. Peter Anvin" <hpa@zytor.com>,
        Borislav Petkov <bp@suse.de>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] x86/kexec: Make kexec work in 5-level paging mode
Message-ID: <20180129115927.GB18247@bombadil.infradead.org>
References: <20180129110845.26633-1-kirill.shutemov@linux.intel.com>
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On Mon, Jan 29, 2018 at 02:08:45PM +0300, Kirill A. Shutemov wrote:
> I've missed that we need to change relocate_kernel() to set CR4.LA57
> flag if the kernel has 5-level paging enabled.
> 
> I avoided to use ifdef CONFIG_X86_5LEVEL here and inferred if we need to
> enabled 5-level paging from previous CR4 value. This way the code is
> ready for boot-time switching between paging modes.

Forgive me if I'm missing something ... can you kexec a 5-level kernel
from a 4-level kernel or vice versa?