On Tue, 12 Mar 2019, Baoquan He wrote: > In relocate_kernel() CR4.LA57 flag is set before kexec jumping if > the kernel has 5-level paging enabled. Then in boot/compressed/head_64.S, > it will check if the booting kernel is in 4-level or 5-level paging > mode, and handle accordingly. However, the old kernel which doesn't > contain the 5-level codes doesn't know how to cope with it, then #GP > triggered.
The above is more than confusing. I assume you want to say: If the running kernel has 5-level paging activated, the 5-level paging mode is preserved across kexec. If the kexec'ed kernel does not contain support for handling active 5-level paging mode in the decompressor, the decompressor will crash with #GP. > Instead of triggering #GP during kexec kernel boot, error out during > kexec loading if find out we are trying to jump to old 4-level kernel > from 5-level kernel. Prevent this situation at load time. If 5-level paging is active, check the xloadflags whether the kexec kernel can handle 5-level paging at least in the decompressor. If not, reject the load attempt. > Signed-off-by: Baoquan He <b...@redhat.com> > Acked-by: Kirill A. Shutemov <kirill.shute...@linux.intel.com> > --- > arch/x86/kernel/kexec-bzimage64.c | 5 +++++ > 1 file changed, 5 insertions(+) > > diff --git a/arch/x86/kernel/kexec-bzimage64.c > b/arch/x86/kernel/kexec-bzimage64.c > index 1f3b77367948..4c9c079b5673 100644 > --- a/arch/x86/kernel/kexec-bzimage64.c > +++ b/arch/x86/kernel/kexec-bzimage64.c > @@ -321,6 +321,11 @@ static int bzImage64_probe(const char *buf, unsigned > long len) > return ret; > } > > + if (!(header->xloadflags & XLF_5LEVEL) && pgtable_l5_enabled()) { > + pr_err("Can not jump to old 4-level kernel from 5-level > kernel.\n"); This is confusing at best. "bzImage cannot handle 5-level paging mode\n" or something like this. > + return ret; Thanks, tglx