On Sun, Dec 17, 2017 at 08:34:52PM +0100, Patrick Wildt wrote: > Hi, > > I had been looking into booting a 32-bit kernel with efiboot and the > first thing I stumbled upon is that when we jump back into 32-bit mode > we don't disable the Long Mode Extension. Thus when the i386 kernel > turns on paging, LME goes active as well and "weird things happen". > > Not sure this path is worth pursuing, but this diff at least resets > EFER correctly. > > Opinions? ok? > > Patrick > > diff --git a/sys/arch/amd64/stand/efiboot/run_i386.S > b/sys/arch/amd64/stand/efiboot/run_i386.S > index 1c70f8d4610..63d6f1f1dca 100644 > --- a/sys/arch/amd64/stand/efiboot/run_i386.S > +++ b/sys/arch/amd64/stand/efiboot/run_i386.S > @@ -88,6 +88,12 @@ start32a: > andl $(~CR4_PAE), %eax > movl %eax, %cr4 > > + /* Disable LME */ > + movl $MSR_EFER, %ecx > + rdmsr > + xor %eax, %eax > + wrmsr > + > jmp start32b > start32b: > .code32 >
Could we ever have the case where EFI set up EFER_NXE? Does that need to be preserved (even in i386 mode)? -ml
