Messages in this thread | | | Date | Mon, 29 Jan 2018 16:48:00 +0300 | From | "Kirill A. Shutemov" <> | Subject | Re: [PATCH] x86/kexec: Make kexec work in 5-level paging mode |
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On Mon, Jan 29, 2018 at 03:59:27AM -0800, Matthew Wilcox wrote: > On Mon, Jan 29, 2018 at 02:08:45PM +0300, Kirill A. Shutemov wrote: > > I've missed that we need to change relocate_kernel() to set CR4.LA57 > > flag if the kernel has 5-level paging enabled. > > > > I avoided to use ifdef CONFIG_X86_5LEVEL here and inferred if we need to > > enabled 5-level paging from previous CR4 value. This way the code is > > ready for boot-time switching between paging modes. > > Forgive me if I'm missing something ... can you kexec a 5-level kernel > from a 4-level kernel or vice versa?
With this patch you can kexec from 4-to-5 and from 5-to-5 in addition to current 4-to-4. 4-to-5 basically takes the same path as UEFI boot in new kernel.
I think I will be able to make 5-to-4 work too, when boot-time switching code will be upstream, assuming both kernels are build from the tree with boot-time switching support and the new kernel is loaded below 128TiB.
For 5-to-4, kernel decompression code of the new kernel starts on 5-level paging identity mapping constructed by caller. Decompression code then would switch over to 4-level paging via 32-bit trampoline (we cannot switch between 4- and 5-level paging directly) and proceed as in normal boot.
Let me check.
-- Kirill A. Shutemov
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