x86/asm/entry: Replace this_cpu_sp0() with current_top_of_stack() and fix it on x86_32
I broke 32-bit kernels. The implementation of sp0 was correct
as far as I can tell, but sp0 was much weirder on x86_32 than I
realized. It has the following issues:
- Init's sp0 is inconsistent with everything else's: non-init tasks
are offset by 8 bytes. (I have no idea why, and the comment is unhelpful.)
- vm86 does crazy things to sp0.
Fix it up by replacing this_cpu_sp0() with
current_top_of_stack() and using a new percpu variable to track
the top of the stack on x86_32.
Signed-off-by: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: 75182b1632a8 ("x86/asm/entry: Switch all C consumers of kernel_stack to this_cpu_sp0()")
Link: http://lkml.kernel.org/r/d09dbe270883433776e0cbee3c7079433349e96d.1425692936.git.luto@amacapital.net
Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index f5e3ec6..48a61c1 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -284,6 +284,10 @@
DECLARE_PER_CPU_SHARED_ALIGNED(struct tss_struct, cpu_tss);
+#ifdef CONFIG_X86_32
+DECLARE_PER_CPU(unsigned long, cpu_current_top_of_stack);
+#endif
+
/*
* Save the original ist values for checking stack pointers during debugging
*/
@@ -564,9 +568,14 @@
#endif
}
-static inline unsigned long this_cpu_sp0(void)
+static inline unsigned long current_top_of_stack(void)
{
+#ifdef CONFIG_X86_64
return this_cpu_read_stable(cpu_tss.x86_tss.sp0);
+#else
+ /* sp0 on x86_32 is special in and around vm86 mode. */
+ return this_cpu_read_stable(cpu_current_top_of_stack);
+#endif
}
#ifdef CONFIG_PARAVIRT