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
