From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wr0-f199.google.com (mail-wr0-f199.google.com [209.85.128.199]) by kanga.kvack.org (Postfix) with ESMTP id C9D6C6B0005 for ; Mon, 29 Jan 2018 08:48:03 -0500 (EST) Received: by mail-wr0-f199.google.com with SMTP id y18so5596259wrh.12 for ; Mon, 29 Jan 2018 05:48:03 -0800 (PST) Received: from mail-sor-f65.google.com (mail-sor-f65.google.com. [209.85.220.65]) by mx.google.com with SMTPS id x38sor5208194eda.41.2018.01.29.05.48.02 for (Google Transport Security); Mon, 29 Jan 2018 05:48:02 -0800 (PST) Date: Mon, 29 Jan 2018 16:48:00 +0300 From: "Kirill A. Shutemov" 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> Sender: owner-linux-mm@kvack.org List-ID: 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 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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org