UefiCpuPkg: Add a 16-bit protected mode code segment descriptor

BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=2198

A hypervisor is not allowed to update an SEV-ES guests register state,
so when booting an SEV-ES guest AP, the hypervisor is not allowed to
set the RIP to the guest requested value. Instead, an SEV-ES AP must be
transition from 64-bit long mode to 16-bit real mode in response to an
INIT-SIPI-SIPI sequence. This requires a 16-bit code segment descriptor.
For PEI, create this descriptor in the reset vector GDT table. For DXE,
create this descriptor from the newly reserved entry at location 0x28.

Cc: Eric Dong <eric.dong@intel.com>
Cc: Ray Ni <ray.ni@intel.com>
Cc: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Eric Dong <eric.dong@intel.com>
Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Regression-tested-by: Laszlo Ersek <lersek@redhat.com>
This commit is contained in:
Tom Lendacky
2020-08-12 15:21:42 -05:00
committed by mergify[bot]
parent 437eb3f7a8
commit 0d7601e546
3 changed files with 15 additions and 6 deletions

View File

@@ -70,14 +70,14 @@ STATIC GDT_ENTRIES GdtTemplate = {
0x0,
},
//
// SPARE4_SEL
// SYS_CODE16_SEL
//
{
0x0, // limit 15:0
0x0FFFF, // limit 15:0
0x0, // base 15:0
0x0, // base 23:16
0x0, // type
0x0, // limit 19:16, flags
0x09A, // present, ring 0, code, execute/read
0x08F, // page-granular, 16-bit
0x0, // base 31:24
},
//