Re: [PATCH] UefiCpuPkg/SecCore: Add pre-memory AP vector

["Ni, Ray" <ray.ni@intel.com>]

Reviewed-by: Ray Ni <ray.ni@intel.com>


> -----Original Message-----
> From: Cole, Deric <deric.cole@intel.com>
> Sent: Wednesday, June 3, 2020 12:42 AM
> To: Ni, Ray <ray.ni@intel.com>; devel@edk2.groups.io
> Cc: Dong, Eric <eric.dong@intel.com>; Laszlo Ersek <lersek@redhat.com>
> Subject: RE: [PATCH] UefiCpuPkg/SecCore: Add pre-memory AP vector
> 
> Ray,
> 
> The NOP is not a functional change, it's just for ease of debug.
> 
> Before, this file was padding with zeros in various places. When viewing this memory using a disassembler, two
> subsequent zero-bytes show up as an ADD instruction, which I found confusing. But worse, if the number of zero-bytes was
> odd, the disassembler might try to "consume" part of the next (real) instruction as an operand to the last hypothetical
> ADD.
> 
> Since NOP is a 1-byte instruction, I used that instead, so it is easier to visually identify the real code versus the padding
> when viewing disassembly.
> 
> -Deric
> 
> -----Original Message-----
> From: Ni, Ray <ray.ni@intel.com>
> Sent: Monday, June 1, 2020 9:51 PM
> To: Cole, Deric <deric.cole@intel.com>; devel@edk2.groups.io
> Cc: Dong, Eric <eric.dong@intel.com>; Laszlo Ersek <lersek@redhat.com>
> Subject: RE: [PATCH] UefiCpuPkg/SecCore: Add pre-memory AP vector
> 
> Deric,
> Can you explain why changing all padding 0x0 to 0x90 (nop) in your patch?
> 
> Is it required to enable AP start up in pre-mem?
> 
> Thanks,
> Ray
> 
> > -----Original Message-----
> > From: Cole, Deric <deric.cole@intel.com>
> > Sent: Tuesday, June 2, 2020 6:32 AM
> > To: devel@edk2.groups.io
> > Cc: Cole, Deric <deric.cole@intel.com>; Dong, Eric
> > <eric.dong@intel.com>; Ni, Ray <ray.ni@intel.com>; Laszlo Ersek
> > <lersek@redhat.com>
> > Subject: [PATCH] UefiCpuPkg/SecCore: Add pre-memory AP vector
> >
> > REF:https://bugzilla.tianocore.org/show_bug.cgi?id=2776
> >
> > Add a vector at 0xFF000 (0xFFFFF000) that can be used by
> > Init-SIPI-SIPI to start an AP before memory is initialized. This
> > vector jumps into the same SEC entry point as the ordinary reset
> > vector, with a special value of "AP" in the DI register. The
> > platform-specific SEC code is expected to check for that value and
> > take a different path for APs, if this feature is supported by the platform.
> >
> > Cc: Eric Dong <eric.dong@intel.com>
> > Cc: Ray Ni <ray.ni@intel.com>
> > Cc: Laszlo Ersek <lersek@redhat.com>
> > Signed-off-by: Deric Cole <deric.cole@intel.com>
> > ---
> >  UefiCpuPkg/SecCore/Ia32/ResetVec.nasmb | 31
> > ++++++++++++++++++++++++-------
> >  1 file changed, 24 insertions(+), 7 deletions(-)
> >
> > diff --git a/UefiCpuPkg/SecCore/Ia32/ResetVec.nasmb
> > b/UefiCpuPkg/SecCore/Ia32/ResetVec.nasmb
> > index f41b9669d0..1dfc4efe4c 100644
> > --- a/UefiCpuPkg/SecCore/Ia32/ResetVec.nasmb
> > +++ b/UefiCpuPkg/SecCore/Ia32/ResetVec.nasmb
> > @@ -10,7 +10,7 @@
> >  ; Abstract:
> >
> >  ;
> >
> >  ;  Reset Vector Data structure
> >
> > -;  This structure is located at 0xFFFFFFC0
> >
> > +;  This structure is located at 0xFFFFF000
> >
> >  ;
> >
> >
> > ;---------------------------------------------------------------------
> > ---------
> >
> >
> >
> > @@ -23,19 +23,36 @@ USE16
> >  ;
> >
> >
> >
> >      ORG     0h
> >
> > +
> >
> > +;
> >
> > +; 0xFFFFF000
> >
> > +;
> >
> > +; We enter here with CS:IP = 0xFF00:0x0000. Do a far-jump to change
> > +CS to
> > 0xF000
> >
> > +; and IP to ApStartup.
> >
> > +;
> >
> > +ApVector:
> >
> > +    mov     di, "AP"
> >
> > +    jmp     0xF000:0xF000+ApStartup
> >
> > +
> >
> > +    TIMES 0xFC0-($-$$) nop
> >
> > +
> >
> > +;
> >
> > +; This should be at 0xFFFFFFC0
> >
> > +;
> >
> > +
> >
> >  ;
> >
> >  ; Reserved
> >
> >  ;
> >
> >  ReservedData:            DD 0eeeeeeeeh, 0eeeeeeeeh
> >
> >
> >
> > -    TIMES 0x10-($-$$) DB 0
> >
> > +    TIMES 0xFD0-($-$$) nop
> >
> >  ;
> >
> > -; This is located at 0xFFFFFFD0h
> >
> > +; This is located at 0xFFFFFFD0
> >
> >  ;
> >
> >      mov     di, "PA"
> >
> >      jmp     ApStartup
> >
> >
> >
> > -    TIMES 0x20-($-$$) DB 0
> >
> > +    TIMES 0xFE0-($-$$) nop
> >
> >  ;
> >
> >  ; Pointer to the entry point of the PEI core
> >
> >  ; It is located at 0xFFFFFFE0, and is fixed up by some build tool
> >
> > @@ -53,7 +70,7 @@ ASM_PFX(InterruptHandler):
> >      jmp     $
> >
> >      iret
> >
> >
> >
> > -    TIMES 0x30-($-$$) DB 0
> >
> > +    TIMES 0xFF0-($-$$) nop
> >
> >  ;
> >
> >  ; For IA32, the reset vector must be at 0xFFFFFFF0, i.e., 4G-16 byte
> >
> >  ; Execution starts here upon power-on/platform-reset.
> >
> > @@ -74,7 +91,7 @@ ApStartup:
> >      DW      -3
> >
> >
> >
> >
> >
> > -    TIMES 0x38-($-$$) DB 0
> >
> > +    TIMES 0xFF8-($-$$) nop
> >
> >  ;
> >
> >  ; Ap reset vector segment address is at 0xFFFFFFF8
> >
> >  ; This will be fixed up by some build tool,
> >
> > @@ -83,7 +100,7 @@ ApStartup:
> >  ;
> >
> >  ApSegAddress:    dd      12345678h
> >
> >
> >
> > -    TIMES 0x3c-($-$$) DB 0
> >
> > +    TIMES 0xFFC-($-$$) nop
> >
> >  ;
> >
> >  ; BFV Base is at 0xFFFFFFFC
> >
> >  ; This will be fixed up by some build tool,
> >
> > --
> > 2.26.2.windows.1
> 
>