[patch] x86/realmode: Make stack lock work in trampoline_compat()

Thomas Gleixner
2023-05-30T10:46:57Z

The stack locking and stack assignment macro LOAD_REALMODE_ESP fails to
work when invoked from the 64bit trampoline entry point:

trampoline_start64
trampoline_compat
LOAD_REALMODE_ESP <- lock

Accessing tr_lock is only possible from 16bit mode. For the compat entry
point this needs to be pa_tr_lock so that the required relocation entry is
generated. Otherwise it locks the non-relocated address which is
aside of being wrong never cleared in secondary_startup_64() causing all
but the first CPU to get stuck on the lock.

Make the macro take an argument lock_pa which defaults to 0 and rename it
to LOCK_AND_LOAD_REALMODE_ESP to make it clear what this is about.

Fixes: f6f1ae9128d2 ("x86/smpboot: Implement a bit spinlock to protect the realmode stack")
Reported-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
arch/x86/realmode/rm/trampoline_64.S | 12 ++++++++----
1 file changed, 8 insertions(+), 4 deletions(-)

--- a/arch/x86/realmode/rm/trampoline_64.S
+++ b/arch/x86/realmode/rm/trampoline_64.S
@@ -37,12 +37,16 @@
.text
.code16

-.macro LOAD_REALMODE_ESP
+.macro LOCK_AND_LOAD_REALMODE_ESP lock_pa=0
/*
* Make sure only one CPU fiddles with the realmode stack
*/
.Llock_rm\@:
+ .if \lock_pa
+ lock btsl $0, pa_tr_lock
+ .else
lock btsl $0, tr_lock
+ .endif
jnc 2f
pause
jmp .Llock_rm\@
@@ -63,7 +67,7 @@ SYM_CODE_START(trampoline_start)
mov %ax, %es
mov %ax, %ss

- LOAD_REALMODE_ESP
+ LOCK_AND_LOAD_REALMODE_ESP

call verify_cpu # Verify the cpu supports long mode
testl %eax, %eax # Check for return code
@@ -106,7 +110,7 @@ SYM_CODE_START(sev_es_trampoline_start)
mov %ax, %es
mov %ax, %ss

- LOAD_REALMODE_ESP
+ LOCK_AND_LOAD_REALMODE_ESP

jmp .Lswitch_to_protected
SYM_CODE_END(sev_es_trampoline_start)
@@ -189,7 +193,7 @@ 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.
*/
- LOAD_REALMODE_ESP
+ LOCK_AND_LOAD_REALMODE_ESP lock_pa=1
movw $__KERNEL_DS, %dx

movl $(CR0_STATE & ~X86_CR0_PG), %eax