On 09/03/18 at 10:46pm, H. Peter Anvin wrote: > 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. OK, I didn't get your point. I forget what difficulty was met so that Kirill need to take this way. In that way, we will never have chance to put kernel above 64TB even from 5-level kernel to jump to 5-level kernel. Hi Kirill, Could you help to explain why the current implementation is decided? Thanks Baoquan _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
