diff options
| -rw-r--r-- | Documentation/arch/x86/index.md | 1 | ||||
| -rw-r--r-- | src/cpu/x86/64bit/exit32.inc | 84 | ||||
| -rw-r--r-- | src/cpu/x86/smm/smmhandler.S | 46 |
3 files changed, 130 insertions, 1 deletions
diff --git a/Documentation/arch/x86/index.md b/Documentation/arch/x86/index.md index 30dcc10e91..f5546d18d5 100644 --- a/Documentation/arch/x86/index.md +++ b/Documentation/arch/x86/index.md @@ -45,6 +45,7 @@ At the moment *$n* is 4, which results in identity mapping the lower 4 GiB. * Add x86_64 exception handlers - *DONE* * Setup page tables for long mode - *DONE* * Add assembly code for long mode - *DONE* +* Add assembly code for SMM - *DONE* * Add assembly code for postcar stage - *TODO* * Add assembly code to return to protected mode - *TODO* * Implement reference code for mainboard `emulation/qemu-q35` - *TODO* diff --git a/src/cpu/x86/64bit/exit32.inc b/src/cpu/x86/64bit/exit32.inc new file mode 100644 index 0000000000..48837d96a9 --- /dev/null +++ b/src/cpu/x86/64bit/exit32.inc @@ -0,0 +1,84 @@ +/* SPDX-License-Identifier: GPL-2.0-only */ + +/* + * For droping from long mode to protected mode. + * + * For reference see "AMD64 ArchitectureProgrammer's Manual Volume 2", + * Document 24593-Rev. 3.31-July 2019 Chapter 5.3 + * + * Clobbers: rax, rbx, rcx, rdx + */ +.code64 + +#include <cpu/x86/msr.h> +#include <cpu/x86/cr.h> +#include <arch/rom_segs.h> + +drop_longmode: + /* Ensure cache is clean. */ + wbinvd + + /* Set 32-bit code segment and ss */ + mov $ROM_CODE_SEG, %rcx + /* SetCodeSelector32 will drop us to protected mode on return */ + call SetCodeSelector32 + + /* Skip SetCodeSelector32 */ +.code32 + jmp __longmode_compatibility + +.align 8 +.code64 +SetCodeSelector32: + # pop the return address from stack + pop %rbx + + # save rsp because we need to push it after ss + mov %rsp, %rdx + + # use iret to jump to a 32-bit offset in a new code segment + # iret will pop cs:rip, flags, then ss:rsp + mov %ss, %ax # need to push ss, but push ss instuction + push %rax # not valid in x64 mode, so use ax + push %rdx # the rsp to load + pushfq # push rflags + push %rcx # cx is code segment selector from caller + push %rbx # push the IP for the next instruction + + # the iretq will behave like ret, with the new cs/ss value loaded + iretq + +.align 4 +.code32 +__longmode_compatibility: + /* Running in 32-bit compatibility mode */ + + /* Use flat data segment */ + movl $ROM_DATA_SEG, %eax + movl %eax, %ds + movl %eax, %es + movl %eax, %ss + movl %eax, %fs + movl %eax, %gs + + /* Disable paging. */ + movl %cr0, %eax + andl $(~CR0_PG), %eax + movl %eax, %cr0 + + /* Disable long mode. */ + movl $(IA32_EFER), %ecx + rdmsr + andl $(~EFER_LME), %eax + wrmsr + + /* Disable PAE. */ + movl %cr4, %eax + andl $(~CR4_PAE), %eax + movl %eax, %cr4 + + /* Clear page table register */ + xor %eax, %eax + movl %eax, %cr3 + +__longmode_exit: diff --git a/src/cpu/x86/smm/smmhandler.S b/src/cpu/x86/smm/smmhandler.S index 036bc83e2f..340840f685 100644 --- a/src/cpu/x86/smm/smmhandler.S +++ b/src/cpu/x86/smm/smmhandler.S @@ -8,6 +8,7 @@ */ #include <cpu/x86/lapic_def.h> +#include <cpu/x86/msr.h> /* * +--------------------------------+ 0xaffff @@ -42,6 +43,14 @@ #define SMM_HANDLER_OFFSET 0x0000 +#if defined(__x86_64__) +.bss +ia32efer_backup_eax: +.long +ia32efer_backup_edx: +.long +#endif + /* initially SMM is some sort of real mode. Let gcc know * how to treat the SMM handler stub */ @@ -159,12 +168,44 @@ untampered_lapic: /* Get SMM revision */ movl $0xa8000 + 0x7efc, %ebx /* core 0 address */ subl %ebp, %ebx /* subtract core X offset */ + +#if defined(__x86_64__) + /* Backup IA32_EFER. Preserves ebx. */ + movl $(IA32_EFER), %ecx + rdmsr + movl %eax, ia32efer_backup_eax + movl %edx, ia32efer_backup_edx + + /* Enable long mode. Preserves ebx. */ +#include <cpu/x86/64bit/entry64.inc> + + mov (%ebx), %rdi + +#else movl (%ebx), %eax pushl %eax +#endif - /* Call 32bit C handler */ + /* Call C handler */ call smi_handler +#if defined(__x86_64__) + /* + * The only reason to go back to protected mode is that RSM doesn't restore + * MSR registers and MSR IA32_EFER was modified by entering long mode. + * Drop to protected mode to safely operate on the IA32_EFER MSR. + */ + + /* Disable long mode. */ + #include <cpu/x86/64bit/exit32.inc> + + /* Restore IA32_EFER as RSM doesn't restore MSRs. */ + movl $(IA32_EFER), %ecx + movl ia32efer_backup_eax, %eax + movl ia32efer_backup_edx, %edx + wrmsr +#endif + /* To return, just do rsm. It will "clean up" protected mode */ rsm @@ -190,6 +231,9 @@ smm_gdt: .word 0xffff, 0x0000 .byte 0x00, 0x93, 0xcf, 0x00 + /* gdt selector 0x18, flat code segment (64-bit) */ + .word 0xffff, 0x0000 + .byte 0x00, 0x9b, 0xaf, 0x00 smm_gdt_end: |