x86/asm/entry: Switch all C consumers of kernel_stack to this_cpu_sp0()

amluto · Ingo Molnar · commit 75182b1632a8 · 2015-03-06T08:32:57.000+01:00
This will make modifying the semantics of kernel_stack easier. The change to ist_begin_non_atomic() is necessary because sp0 no longer points to the same THREAD_SIZE-aligned region as RSP; it's one byte too high for that. At Denys' suggestion, rather than offsetting it, just check explicitly that we're in the correct range ending at sp0. This has the added benefit that we no longer assume that the thread stack is aligned to THREAD_SIZE. Suggested-by: Denys Vlasenko <dvlasenk@redhat.com> Signed-off-by: Andy Lutomirski <luto@amacapital.net> Cc: Borislav Petkov <bp@alien8.de> 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> Link: http://lkml.kernel.org/r/ef8254ad414cbb8034c9a56396eeb24f5dd5b0de.1425611534.git.luto@amacapital.net Signed-off-by: Ingo Molnar <mingo@kernel.org>
diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
@@ -159,8 +159,7 @@ DECLARE_PER_CPU(unsigned long, kernel_stack);
 static inline struct thread_info *current_thread_info(void)
 {
 	struct thread_info *ti;
-	ti = (void *)(this_cpu_read_stable(kernel_stack) +
-		      KERNEL_STACK_OFFSET - THREAD_SIZE);
+	ti = (void *)(this_cpu_sp0() - THREAD_SIZE);
 	return ti;
 }
 
diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
@@ -174,8 +174,8 @@ void ist_begin_non_atomic(struct pt_regs *regs)
 	 * will catch asm bugs and any attempt to use ist_preempt_enable
 	 * from double_fault.
 	 */
-	BUG_ON(((current_stack_pointer() ^ this_cpu_read_stable(kernel_stack))
-		& ~(THREAD_SIZE - 1)) != 0);
+	BUG_ON((unsigned long)(this_cpu_sp0() - current_stack_pointer()) >=
+	       THREAD_SIZE);
 
 	preempt_count_sub(HARDIRQ_OFFSET);
 }

Original file line number	Diff line number	Diff line change
`@@ -159,8 +159,7 @@ DECLARE_PER_CPU(unsigned long, kernel_stack);`
`159`	`159`	`static inline struct thread_info *current_thread_info(void)`
`160`	`160`	`{`
`161`	`161`	`struct thread_info *ti;`
`162`		`- ti = (void *)(this_cpu_read_stable(kernel_stack) +`
`163`		`- KERNEL_STACK_OFFSET - THREAD_SIZE);`
	`162`	`+ ti = (void *)(this_cpu_sp0() - THREAD_SIZE);`
`164`	`163`	`return ti;`
`165`	`164`	`}`
`166`	`165`