From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mx3-rdu2.redhat.com ([66.187.233.73] helo=mx1.redhat.com) by bombadil.infradead.org with esmtps (Exim 4.90_1 #2 (Red Hat Linux)) id 1fx3ll-0004p4-2o for kexec@lists.infradead.org; Tue, 04 Sep 2018 05:20:54 +0000 Date: Tue, 4 Sep 2018 13:20:36 +0800 From: Baoquan He Subject: Re: [PATCH 1/3] x86/boot: Add bit fields into xloadflags for 5-level kernel checking Message-ID: <20180904052036.GJ1740@192.168.1.3> References: <20180829141624.13985-1-bhe@redhat.com> <20180829141624.13985-2-bhe@redhat.com> <6ea94875-ae07-6220-eb3e-d3f830cdac03@zytor.com> <20180904034414.GI1740@192.168.1.3> <4546fc39-4982-4c91-c812-0df1e9bc9e20@zytor.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <4546fc39-4982-4c91-c812-0df1e9bc9e20@zytor.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: "H. Peter Anvin" Cc: x86@kernel.org, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, tglx@linutronix.de, mingo@kernel.org, kirill.shutemov@linux.intel.com On 09/03/18 at 09:13pm, H. Peter Anvin wrote: > On 09/03/18 20:44, Baoquan He wrote: > > > > 1) in arch/x86/kernel/relocate_kernel_64.S, we set X86_CR4_LA57 into cr4 > > if the 1st kernel is in 5-level mode. Then in > > arch/x86/boot/compressed/head_64.S, paging_prepare() is called to decide > > if 5-level mode will be enabled, and prepare the trampoline. If > > kexec/kdump kernel is expected to be in 4-level, e.g with 'nolv5' > > specified, it still can handle well. But for the old kernel w/o these > > 5-level codes, it will ignore the fact that X86_CR4_LA57 has been set > > in CR4 and proceed anyway, then #GP is triggered. That's why XLF_5LEVEL > > is used to mark. > > > > That's what I'm saying, don't do that. Always jump into the second kernel in > 4-level mode, i.e. X86_CR4_LA57 unset. That's the only sane thing. Well, this might not be suggested. Kexec has been a formal feature in our distro, our customers usually use it to reboot high end servers because those machines may take one hour to boot up from firmware. And 5-level may be also supported very soon, if people want to do a fast reboot from the current kernel in 5-level, and expect to see it's in 5-level too in the 2nd kernel, this always kexec jumping to the 2nd kernel in 4-level mode might be unaccepted. Thanks Baoquan _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec