From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from terminus.zytor.com ([198.137.202.136] helo=mail.zytor.com) by bombadil.infradead.org with esmtps (Exim 4.90_1 #2 (Red Hat Linux)) id 1fx4D2-0006aG-Na for kexec@lists.infradead.org; Tue, 04 Sep 2018 05:49:05 +0000 Subject: Re: [PATCH 1/3] x86/boot: Add bit fields into xloadflags for 5-level kernel checking 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> <20180904052036.GJ1740@192.168.1.3> From: "H. Peter Anvin" Message-ID: Date: Mon, 3 Sep 2018 22:46:33 -0700 MIME-Version: 1.0 In-Reply-To: <20180904052036.GJ1740@192.168.1.3> Content-Language: en-US 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, tglx@linutronix.de, mingo@kernel.org, kirill.shutemov@linux.intel.com On 09/03/18 22:20, Baoquan He wrote: > 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. > That makes no sense. I'm talking about *entering* the kernel; the second kernel should switch to 5-level mode as necessary. -hpa _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec