On 24/02/2023 15:46, David Woodhouse wrote:
On Fri, 2023-02-24 at 13:59 +0800, Yuan Yao wrote:
+ * Make sure only one CPU fiddles with the realmode stack
+ */
+.Llock_rm:
+ btl $0, tr_lock
+ jnc 2f
+ pause
+ jmp .Llock_rm
+2:
+ lock
+ btsl $0, tr_lock
+ jc .Llock_rm
+
Looks these changes should be applied to trampoline_start64()
yet, which is used for boot up APs when apic->wakeup_secondary_cpu_64
is available, e.g when ACPI_MADT_TYPE_MULTIPROC_WAKEUP is available.
One case I know is the INTEL TD guest, which using the MADT wakeup
for AP wake up now.
Yeah.
I think we could probably pull that all out into a separate asm
"load_realmode_esp" function which takes the lock and actually does the
'movl $rm_stack_end, %esp'.
Then we call it from all the places which currently use $rm_stack_end,
including sev_es_trampoline_start (even though we currently disable
parallel startup there because CPUID doesn't work that early).
Oh... except of course it can't be a function because we haven't got a
stack, have we? It's a macro.
Usama, are you happy using .macro in gas?
Yes, makes sense. I guess something like below should be ok?
It makes sense to add it for sev as well.
diff --git a/arch/x86/realmode/rm/trampoline_64.S
b/arch/x86/realmode/rm/trampoline_64.S
index e38d61d6562e..3a724d8d85b9 100644
--- a/arch/x86/realmode/rm/trampoline_64.S
+++ b/arch/x86/realmode/rm/trampoline_64.S
@@ -38,6 +38,25 @@
.code16
.balign PAGE_SIZE
+
+.macro LOAD_REALMODE_ESP
+ /*
+ * Make sure only one CPU fiddles with the realmode stack
+ */
+.Llock_rm\@:
+ btl $0, tr_lock
+ jnc 2f
+ pause
+ jmp .Llock_rm\@
+2:
+ lock
+ btsl $0, tr_lock
+ jc .Llock_rm\@
+
+ # Setup stack
+ movl $rm_stack_end, %esp
+.endm
+
SYM_CODE_START(trampoline_start)
cli # We should be safe anyway
wbinvd
@@ -49,8 +68,7 @@ SYM_CODE_START(trampoline_start)
mov %ax, %es
mov %ax, %ss
- # Setup stack
- movl $rm_stack_end, %esp
+ LOAD_REALMODE_ESP
call verify_cpu # Verify the cpu supports long mode
testl %eax, %eax # Check for return code
@@ -93,8 +111,7 @@ SYM_CODE_START(sev_es_trampoline_start)
mov %ax, %es
mov %ax, %ss
- # Setup stack
- movl $rm_stack_end, %esp
+ LOAD_REALMODE_ESP
jmp .Lswitch_to_protected
SYM_CODE_END(sev_es_trampoline_start)
@@ -177,7 +194,7 @@ SYM_CODE_START(pa_trampoline_compat)
* In compatibility mode. Prep ESP and DX for startup_32, then
disable
* paging and complete the switch to legacy 32-bit mode.
*/
- movl $rm_stack_end, %esp
+ LOAD_REALMODE_ESP
movw $__KERNEL_DS, %dx
movl $(CR0_STATE & ~X86_CR0_PG), %eax
