Re: [RFC PATCH v3 33/43] MdeModulePkg: Reserve a 16-bit protected mode code segment descriptor

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

Is the 16bit code segment descriptor needed in early DXE before CpuDxe (DXE MP)?

> -----Original Message-----
> From: Tom Lendacky <thomas.lendacky@amd.com>
> Sent: Thursday, November 21, 2019 4:07 AM
> To: devel@edk2.groups.io
> Cc: Justen, Jordan L <jordan.l.justen@intel.com>; Laszlo Ersek <lersek@redhat.com>; Ard Biesheuvel
> <ard.biesheuvel@linaro.org>; Kinney, Michael D <michael.d.kinney@intel.com>; Gao, Liming <liming.gao@intel.com>; Dong,
> Eric <eric.dong@intel.com>; Ni, Ray <ray.ni@intel.com>; Brijesh Singh <brijesh.singh@amd.com>; Wang, Jian J
> <jian.j.wang@intel.com>; Wu, Hao A <hao.a.wu@intel.com>; Bi, Dandan <dandan.bi@intel.com>
> Subject: [RFC PATCH v3 33/43] MdeModulePkg: Reserve a 16-bit protected mode code segment descriptor
> 
> BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=2198
> 
> SEV-ES guest AP boot support needs to transition from 64-bit long mode
> into 16-bit real mode. This will require a 16-bit code segment descriptor.
> Reserve one of the spare segment descriptors (0x28) for this purpose.
> 
> Cc: Jian J Wang <jian.j.wang@intel.com>
> Cc: Hao A Wu <hao.a.wu@intel.com>
> Cc: Dandan Bi <dandan.bi@intel.com>
> Cc: Liming Gao <liming.gao@intel.com>
> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
> ---
>  MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c b/MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c
> index 284b34818ca7..c9cf2e36214f 100644
> --- a/MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c
> +++ b/MdeModulePkg/Core/DxeIplPeim/Ia32/DxeLoadFunc.c
> @@ -33,7 +33,7 @@ GLOBAL_REMOVE_IF_UNREFERENCED IA32_GDT gGdtEntries[] = {
>  /* 0x10 */  {{0xffff, 0,  0,  0xf,  1,  0,  1,  0xf,  0,  0, 1,  1,  0}}, //linear code segment descriptor
>  /* 0x18 */  {{0xffff, 0,  0,  0x3,  1,  0,  1,  0xf,  0,  0, 1,  1,  0}}, //system data segment descriptor
>  /* 0x20 */  {{0xffff, 0,  0,  0xa,  1,  0,  1,  0xf,  0,  0, 1,  1,  0}}, //system code segment descriptor
> -/* 0x28 */  {{0,      0,  0,  0,    0,  0,  0,  0,    0,  0, 0,  0,  0}}, //spare segment descriptor
> +/* 0x28 */  {{0xffff, 0,  0,  0xa,  1,  0,  1,  0xf,  0,  0, 0,  1,  0}}, //system code16 segment descriptor
>  /* 0x30 */  {{0xffff, 0,  0,  0x2,  1,  0,  1,  0xf,  0,  0, 1,  1,  0}}, //system data segment descriptor
>  /* 0x38 */  {{0xffff, 0,  0,  0xa,  1,  0,  1,  0xf,  0,  1, 0,  1,  0}}, //system code segment descriptor
>  /* 0x40 */  {{0,      0,  0,  0,    0,  0,  0,  0,    0,  0, 0,  0,  0}}, //spare segment descriptor
> --
> 2.17.1