From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mail-pg1-x543.google.com ([2607:f8b0:4864:20::543]) by bombadil.infradead.org with esmtps (Exim 4.90_1 #2 (Red Hat Linux)) id 1fvNTc-0003zL-J8 for kexec@lists.infradead.org; Thu, 30 Aug 2018 13:59:19 +0000 Received: by mail-pg1-x543.google.com with SMTP id r1-v6so3921798pgp.11 for ; Thu, 30 Aug 2018 06:59:02 -0700 (PDT) Date: Thu, 30 Aug 2018 16:58:56 +0300 From: "Kirill A. Shutemov" Subject: Re: [PATCH 0/3] Add restrictions for kexec/kdump jumping between 5-level and 4-level kernel Message-ID: <20180830135855.rylamc7mx2ur3tab@kshutemo-mobl1> References: <20180829141624.13985-1-bhe@redhat.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20180829141624.13985-1-bhe@redhat.com> List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kexec" Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: Baoquan He Cc: x86@kernel.org, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, hpa@zytor.com, tglx@linutronix.de, mingo@kernel.org, kirill.shutemov@linux.intel.com On Wed, Aug 29, 2018 at 10:16:21PM +0800, Baoquan He wrote: > This was suggested by Kirill several months ago, I worked out several > patches to fix, then interrupted by other issues. So sort them out > now and post for reviewing. Thanks for doing this. > The current upstream kernel supports 5-level paging mode and supports > dynamically choosing paging mode during bootup according to kernel > image, hardware and kernel parameter setting. This flexibility brings > several issues for kexec/kdump: > 1) > Switching between paging modes, requires changes into target kernel. > It means you cannot kexec() 4-level paging kernel from 5-level paging > kernel if 4-level paging kernel doesn't include changes. > > 2) > Switching from 5-level paging to 4-level paging kernel would fail, if > kexec() put kernel image above 64TiB of memory. I'm not entirely sure that 64TiB is the limit here. Technically, 4-level paging allows to address 256TiB in 1-to-1 mapping. We just don't have machines with that wide physical address space (which don't support 5-level paging too). What is your reasoning about 64TiB limit? -- Kirill A. Shutemov _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec