Re: crash in entry.S restore_all, 2.6.12-rc2, x86, PAGEALLOC

[Stas Sergeev <stsp@aknet.ru>]

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Hi Ingo et all.

Ingo Molnar wrote:
> the crashes below happen when PAGEALLOC is enabled. It's this 
> instruction:
>  movb OLDSS(%esp), %ah
I am really sorry about that screwup :(
I can't do too much right now as I am
reading the mail in a batch mode, and
the next time I'll be reading it will
be 24 hours from now.

Attached is a quick fix, which I'll be
testing to death tomorrow at work.
I had DEBUG_PAGEALLOC disabled, so I
haven't noticed that stupid bug while
optimizing my checks...
Let me know how it goes. 


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--- entry.S.old	2005-04-05 20:08:07.000000000 +0400
+++ entry.S	2005-04-05 22:54:43.000000000 +0400
@@ -244,11 +244,12 @@
 	jne syscall_exit_work
 
 restore_all:
-	movl EFLAGS(%esp), %eax		# mix EFLAGS, SS and CS
-	movb OLDSS(%esp), %ah
-	movb CS(%esp), %al
-	andl $(VM_MASK | (4 << 8) | 3), %eax
-	cmpl $((4 << 8) | 3), %eax
+	testl $3, CS(%esp)
+	jz restore_nocheck		# return to kernel or v86
+	movl EFLAGS(%esp), %eax		# mix EFLAGS and SS
+	movb OLDSS(%esp), %al
+	andl $(VM_MASK | 4), %eax
+	cmpl $4, %eax
 	je ldt_ss			# returning to user-space with LDT SS
 restore_nocheck:
 	RESTORE_REGS