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 -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
