* David Woodhouse <dwmw2@xxxxxxxxxxxxx> wrote: > From: David Woodhouse <dwmw@xxxxxxxxxxxx> > > There are some failure modes which lead to triple-faults in the > relocate_kernel function, which is fairly much undebuggable for normal > mortals. > > Adding a GDT in the relocate_kernel environment is step 1 towards being > able to catch faults and do something more useful. > > Signed-off-by: David Woodhouse <dwmw@xxxxxxxxxxxx> > --- > arch/x86/kernel/relocate_kernel_64.S | 27 +++++++++++++++++++++++++++ > 1 file changed, 27 insertions(+) > > diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S > index af2cd06ff318..c62f03808f18 100644 > --- a/arch/x86/kernel/relocate_kernel_64.S > +++ b/arch/x86/kernel/relocate_kernel_64.S > @@ -39,6 +39,18 @@ SYM_DATA(kexec_pa_table_page, .quad 0) > SYM_DATA(kexec_pa_swap_page, .quad 0) > SYM_DATA_LOCAL(pa_backup_pages_map, .quad 0) > > +#ifdef CONFIG_KEXEC_DEBUG > + .balign 16 > +SYM_DATA_START_LOCAL(kexec_debug_gdt) > + .word kexec_debug_gdt_end - kexec_debug_gdt - 1 > + .long 0 > + .word 0 > + .quad 0x00cf9a000000ffff /* __KERNEL32_CS */ > + .quad 0x00af9a000000ffff /* __KERNEL_CS */ > + .quad 0x00cf92000000ffff /* __KERNEL_DS */ > +SYM_DATA_END_LABEL(kexec_debug_gdt, SYM_L_LOCAL, kexec_debug_gdt_end) > +#endif /* CONFIG_KEXEC_DEBUG */ Yeah, so is there any reason (other than paranoia) why the early-early GDT and IDT shouldn't be unconditional? There's many ways for such an approach to bitrot, it's much better to not hide it behind a default-disabled debug option... Some of the other bits, like the hard-coded serial debugging assumptions, probably need to be behind the debug option - but much of the new debug mechanism looks safe and generic and can be always-on, IMHO. This would also throw regressions back into the face of whoever manages to introduce them, ideally. ;-) Thanks, Ingo
