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@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
