%es is used implicitly by string instructions. On June 12, 2015 12:50:13 AM PDT, Ingo Molnar <mi...@kernel.org> wrote: > >* Andy Lutomirski <l...@amacapital.net> wrote: > >> > --- a/arch/x86/kernel/acpi/wakeup_32.S >> > +++ b/arch/x86/kernel/acpi/wakeup_32.S >> > @@ -81,6 +81,10 @@ ENTRY(do_suspend_lowlevel) >> > jmp ret_point >> > .p2align 4,,7 >> > ret_point: >> > + /* In case the BIOS corrupted DS, make the kernel context >minimally functional: */ >> > + movl $__KERNEL_DS, %eax >> > + movl %eax, %ds >> > + >> >> On further thought, I think you want movl $__USER_DS, %eax. The >> 32-bit kernel is a strange beast. Also, you should probably fix up >> %es as well. > >So restore_processor_state() already restores ES. The idea here was to >reload DS >early on, because the kernel implicitly uses it for data access so we >need it to >be good to be able to continue executing any generic kernel code. > >We don't use %es: prefixed assembly AFAICS, what are the implicit users >of ES? > >Also, to further confuse things, we also have: > >ENTRY(wakeup_pmode_return) >wakeup_pmode_return: > movw $__KERNEL_DS, %ax > movw %ax, %ss > movw %ax, %ds > movw %ax, %es > movw %ax, %fs > movw %ax, %gs > > # reload the gdt, as we need the full 32 bit address > lidt saved_idt > lldt saved_ldt > ljmp $(__KERNEL_CS), $1f >1: > movl %cr3, %eax > movl %eax, %cr3 > wbinvd > >which seems to be another layer of restoration - but it possibly does >not trigger >in the S2RAM case here. > >Oh, funny the 'reload the gdt' comment: do you see an LGDT there? It >reloads all >segment selectors, the IDT, LDT and CR3, but does not seem to reload >the GDT - the >only thing the comment describes. > >Thanks, > > Ingo
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