[tip: x86/asm] x86/asm/suspend: Get rid of bogus_64_magic

[tip-bot2 for Jiri Slaby]

The following commit has been merged into the x86/asm branch of tip:

Commit-ID:     559ceeed62a5121783a8955c63aeb18aaa0ef224
Gitweb:        https://git.kernel.org/tip/559ceeed62a5121783a8955c63aeb18aaa0ef224
Author:        Jiri Slaby <jslaby@xxxxxxx>
AuthorDate:    Fri, 06 Sep 2019 09:55:49 +02:00
Committer:     Borislav Petkov <bp@xxxxxxx>
CommitterDate: Fri, 06 Sep 2019 10:34:15 +02:00

x86/asm/suspend: Get rid of bogus_64_magic

bogus_64_magic is only a dead-end loop. There is no need for an
out-of-order function (and unannotated local label), so just handle it
in-place and also store 0xbad-m-a-g-i-c to %rcx beforehand, in case
someone is inspecting registers.

Here a qemu+gdb example:

  Remote debugging using localhost:1235
  wakeup_long64 () at arch/x86/kernel/acpi/wakeup_64.S:26
  26              jmp 1b
  (gdb) info registers
  rax            0x123456789abcdef0       1311768467463790320
  rbx            0x0      0
  rcx            0xbad6d61676963  3286910041024867
  		 ^^^^^^^^^^^^^^^

 [ bp: Add the gdb example. ]

Signed-off-by: Jiri Slaby <jslaby@xxxxxxx>
Signed-off-by: Borislav Petkov <bp@xxxxxxx>
Cc: "H. Peter Anvin" <hpa@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Len Brown <lenb@xxxxxxxxxx>
Cc: linux-pm@xxxxxxxxxxxxxxx
Cc: Pavel Machek <pavel@xxxxxx>
Cc: "Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: x86-ml <x86@xxxxxxxxxx>
Link: https://lkml.kernel.org/r/20190906075550.23435-1-jslaby@xxxxxxx
---
 arch/x86/kernel/acpi/wakeup_64.S | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/acpi/wakeup_64.S b/arch/x86/kernel/acpi/wakeup_64.S
index b0715c3..7f9ade1 100644
--- a/arch/x86/kernel/acpi/wakeup_64.S
+++ b/arch/x86/kernel/acpi/wakeup_64.S
@@ -18,8 +18,13 @@ ENTRY(wakeup_long64)
 	movq	saved_magic, %rax
 	movq	$0x123456789abcdef0, %rdx
 	cmpq	%rdx, %rax
-	jne	bogus_64_magic
+	je	2f
 
+	/* stop here on a saved_magic mismatch */
+	movq $0xbad6d61676963, %rcx
+1:
+	jmp 1b
+2:
 	movw	$__KERNEL_DS, %ax
 	movw	%ax, %ss	
 	movw	%ax, %ds
@@ -37,9 +42,6 @@ ENTRY(wakeup_long64)
 	jmp	*%rax
 ENDPROC(wakeup_long64)
 
-bogus_64_magic:
-	jmp	bogus_64_magic
-
 ENTRY(do_suspend_lowlevel)
 	FRAME_BEGIN
 	subq	$8, %rsp