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

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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
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9
UefiCpuPkg/ResetVector/Vtf0/Ia16/Real16ToFlat32.asm
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@@ -129,5 +129,14 @@ LINEAR_CODE64_SEL equ $-GDT_BASE
DB 0 ; base 31:24
%endif
; linear code segment descriptor
LINEAR_CODE16_SEL equ $-GDT_BASE
DW 0xffff ; limit 15:0
DW 0 ; base 15:0
DB 0 ; base 23:16
DB PRESENT_FLAG(1)|DPL(0)|SYSTEM_FLAG(1)|DESC_TYPE(CODE32_TYPE)
DB GRANULARITY_FLAG(1)|DEFAULT_SIZE32(0)|CODE64_FLAG(0)|UPPER_LIMIT(0xf)
DB 0 ; base 31:24
GDT_END: