Hi hpa, Thanks for looking into this.
On 09/03/18 at 07:41pm, H. Peter Anvin wrote: > I don't understand why there is any reason not to always enter the target > kernel in 4-level mode. There certainly is no point whatsoever in having two > xloadflags: the only thing that could possibly matter is whether or not the > kernel in question *can* be entered in 5-level mode should that ever be > necessary. This patchset is only used to fix kexec/kdump issues. We never stop kernel booting in 4-level mode from firmware as 1st kernel. However, there are issues when jump from the 1st kernel which is in 5-level mode to 2nd kernel. The reason is: 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. 2) For kexec_load interface, we put kernel/initrd at top of system RAM in kexec_tools utility. If the 1st kernel is in 5-level mode, the kexec-ed kernel has "CONFIG_X86_5LEVEL=n", we have to detect this and limit the kernel to be loaded under 64TB, since kexec-ed kernel will definitely run in 4-level mode. Putting kernel above 64TB will fail kexec-ed kernel booting. That's why *XLF_5LEVEL_ENABLED* is needed. Thanks Baoquan _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec
