Re: [PATCH 1/1] OvmfPkg/Bhyve: Copy Real16ToFlat32.asm and enable cache in CR0


Peter Grehan
 

Reviewed-by: Peter Grehan <grehan@freebsd.org>

Copy UefiCpuPkg/ResetVector/Vtf0/Ia16/Real16ToFlat32.asm to
OvmfPkg/Bhyve/ResetVector/Ia16, with one change, as has also been
made in XenResetVector:
- SEC_DEFAULT_CR0: enable cache (bit 30 or CD set to 0)
With the CD bit set to 1, this has the downside on AMD systems of
actually running with the cache disabled, which slows the entire system
to a crawl.
There's no need for this bit to be set in virtualized
environments.
This patch reapplies the change from the freebsd uefi-edk2 repo at
https://github.com/freebsd/uefi-edk2/commit/08c00f4e8d9e3e469bdc2ce92d3aa839cae7cf17
Signed-off-by: Rebecca Cran <rebecca@bsdio.com>
---
.../Bhyve/ResetVector/Ia16/Real16ToFlat32.asm | 142 ++++++++++++++++++
1 file changed, 142 insertions(+)
create mode 100644 OvmfPkg/Bhyve/ResetVector/Ia16/Real16ToFlat32.asm
diff --git a/OvmfPkg/Bhyve/ResetVector/Ia16/Real16ToFlat32.asm b/OvmfPkg/Bhyve/ResetVector/Ia16/Real16ToFlat32.asm
new file mode 100644
index 000000000000..fe377ac842f4
--- /dev/null
+++ b/OvmfPkg/Bhyve/ResetVector/Ia16/Real16ToFlat32.asm
@@ -0,0 +1,142 @@
+;------------------------------------------------------------------------------
+; @file
+; Transition from 16 bit real mode into 32 bit flat protected mode
+;
+; Copyright (c) 2008 - 2010, Intel Corporation. All rights reserved.<BR>
+; SPDX-License-Identifier: BSD-2-Clause-Patent
+;
+;------------------------------------------------------------------------------
+
+%define SEC_DEFAULT_CR0 0x00000023
+%define SEC_DEFAULT_CR4 0x640
+
+BITS 16
+
+;
+; Modified: EAX, EBX
+;
+; @param[out] DS Selector allowing flat access to all addresses
+; @param[out] ES Selector allowing flat access to all addresses
+; @param[out] FS Selector allowing flat access to all addresses
+; @param[out] GS Selector allowing flat access to all addresses
+; @param[out] SS Selector allowing flat access to all addresses
+;
+TransitionFromReal16To32BitFlat:
+
+ debugShowPostCode POSTCODE_16BIT_MODE
+
+ cli
+
+ mov bx, 0xf000
+ mov ds, bx
+
+ mov bx, ADDR16_OF(gdtr)
+
+o32 lgdt [cs:bx]
+
+ mov eax, SEC_DEFAULT_CR0
+ mov cr0, eax
+
+ jmp LINEAR_CODE_SEL:dword ADDR_OF(jumpTo32BitAndLandHere)
+BITS 32
+jumpTo32BitAndLandHere:
+
+ mov eax, SEC_DEFAULT_CR4
+ mov cr4, eax
+
+ debugShowPostCode POSTCODE_32BIT_MODE
+
+ mov ax, LINEAR_SEL
+ mov ds, ax
+ mov es, ax
+ mov fs, ax
+ mov gs, ax
+ mov ss, ax
+
+ OneTimeCallRet TransitionFromReal16To32BitFlat
+
+ALIGN 2
+
+gdtr:
+ dw GDT_END - GDT_BASE - 1 ; GDT limit
+ dd ADDR_OF(GDT_BASE)
+
+ALIGN 16
+
+;
+; Macros for GDT entries
+;
+
+%define PRESENT_FLAG(p) (p << 7)
+%define DPL(dpl) (dpl << 5)
+%define SYSTEM_FLAG(s) (s << 4)
+%define DESC_TYPE(t) (t)
+
+; Type: data, expand-up, writable, accessed
+%define DATA32_TYPE 3
+
+; Type: execute, readable, expand-up, accessed
+%define CODE32_TYPE 0xb
+
+; Type: execute, readable, expand-up, accessed
+%define CODE64_TYPE 0xb
+
+%define GRANULARITY_FLAG(g) (g << 7)
+%define DEFAULT_SIZE32(d) (d << 6)
+%define CODE64_FLAG(l) (l << 5)
+%define UPPER_LIMIT(l) (l)
+
+;
+; The Global Descriptor Table (GDT)
+;
+
+GDT_BASE:
+; null descriptor
+NULL_SEL equ $-GDT_BASE
+ DW 0 ; limit 15:0
+ DW 0 ; base 15:0
+ DB 0 ; base 23:16
+ DB 0 ; sys flag, dpl, type
+ DB 0 ; limit 19:16, flags
+ DB 0 ; base 31:24
+
+; linear data segment descriptor
+LINEAR_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(DATA32_TYPE)
+ DB GRANULARITY_FLAG(1)|DEFAULT_SIZE32(1)|CODE64_FLAG(0)|UPPER_LIMIT(0xf)
+ DB 0 ; base 31:24
+
+; linear code segment descriptor
+LINEAR_CODE_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(1)|CODE64_FLAG(0)|UPPER_LIMIT(0xf)
+ DB 0 ; base 31:24
+
+%ifdef ARCH_X64
+; linear code (64-bit) segment descriptor
+LINEAR_CODE64_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(CODE64_TYPE)
+ DB GRANULARITY_FLAG(1)|DEFAULT_SIZE32(0)|CODE64_FLAG(1)|UPPER_LIMIT(0xf)
+ 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:
+

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