[SeaBIOS] [PATCH 1/4] smm: Backup and restore A20 on an SMI based mode switch
Kevin O'Connor
kevin at koconnor.net
Tue May 16 18:14:48 CEST 2017
QEMU does not store the A20 setting in the SMM cpu environment area
(and it does not look like real CPUs do either). So, manually backup
and restore A20 on a mode switch.
Signed-off-by: Kevin O'Connor <kevin at koconnor.net>
---
src/fw/smm.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/src/fw/smm.c b/src/fw/smm.c
index 95f6ba7..178959c 100644
--- a/src/fw/smm.c
+++ b/src/fw/smm.c
@@ -52,7 +52,8 @@ struct smm_state {
struct smm_layout {
struct smm_state backup1;
struct smm_state backup2;
- u8 stack[0x7c00];
+ u32 backup_a20;
+ u8 stack[0x8000 - sizeof(struct smm_state)*2 - sizeof(u32)];
u64 codeentry;
u8 pad_8008[0x7df8];
struct smm_state cpu;
@@ -102,10 +103,13 @@ handle_smi(u16 cs)
memcpy(&smm->cpu, &smm->backup1, sizeof(smm->cpu));
memcpy(&smm->cpu.i32.eax, regs, sizeof(regs));
smm->cpu.i32.eip = regs[3];
+ // Enable a20 and backup its previous state
+ smm->backup_a20 = set_a20(1);
} else if (smm->cpu.i32.ecx == CALL32SMM_RETURNID) {
dprintf(9, "smm cpu ret %x esp=%x\n", regs[3], regs[4]);
memcpy(&smm->cpu, &smm->backup2, sizeof(smm->cpu));
memcpy(&smm->cpu.i32.eax, regs, sizeof(regs));
+ set_a20(smm->backup_a20);
smm->cpu.i32.eip = regs[3];
}
} else if (rev == SMM_REV_I64) {
@@ -116,9 +120,12 @@ handle_smi(u16 cs)
memcpy(&smm->cpu, &smm->backup1, sizeof(smm->cpu));
memcpy(&smm->cpu.i64.rdi, regs, sizeof(regs));
smm->cpu.i64.rip = (u32)regs[4];
+ // Enable a20 and backup its previous state
+ smm->backup_a20 = set_a20(1);
} else if ((u32)smm->cpu.i64.rcx == CALL32SMM_RETURNID) {
memcpy(&smm->cpu, &smm->backup2, sizeof(smm->cpu));
memcpy(&smm->cpu.i64.rdi, regs, sizeof(regs));
+ set_a20(smm->backup_a20);
smm->cpu.i64.rip = (u32)regs[4];
}
}
--
2.9.3
More information about the SeaBIOS
mailing list