From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751864AbeA2NsE (ORCPT ); Mon, 29 Jan 2018 08:48:04 -0500 Received: from mail-wm0-f65.google.com ([74.125.82.65]:37517 "EHLO mail-wm0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751298AbeA2NsD (ORCPT ); Mon, 29 Jan 2018 08:48:03 -0500 X-Google-Smtp-Source: AH8x225u4nSv9RgeClncJecx1YkQnWtStl/wWDdHsDP0uPB4YGUqbctYW3yBl2HBVSSyARlQvASpyQ== Date: Mon, 29 Jan 2018 16:48:00 +0300 From: "Kirill A. Shutemov" To: Matthew Wilcox Cc: "Kirill A. Shutemov" , Ingo Molnar , x86@kernel.org, Thomas Gleixner , "H. Peter Anvin" , Borislav Petkov , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] x86/kexec: Make kexec work in 5-level paging mode Message-ID: <20180129134800.a3sbcqzdy6vd5jjy@node.shutemov.name> References: <20180129110845.26633-1-kirill.shutemov@linux.intel.com> <20180129115927.GB18247@bombadil.infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180129115927.GB18247@bombadil.infradead.org> User-Agent: NeoMutt/20171215 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Jan 29, 2018 at 03:59:27AM -0800, Matthew Wilcox wrote: > 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? With this patch you can kexec from 4-to-5 and from 5-to-5 in addition to current 4-to-4. 4-to-5 basically takes the same path as UEFI boot in new kernel. I think I will be able to make 5-to-4 work too, when boot-time switching code will be upstream, assuming both kernels are build from the tree with boot-time switching support and the new kernel is loaded below 128TiB. For 5-to-4, kernel decompression code of the new kernel starts on 5-level paging identity mapping constructed by caller. Decompression code then would switch over to 4-level paging via 32-bit trampoline (we cannot switch between 4- and 5-level paging directly) and proceed as in normal boot. Let me check. -- Kirill A. Shutemov