[PATCH v2 2/6] x86: Switch all C consumers of kernel_stack to this_cpu_sp0

[Andy Lutomirski]

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.

Signed-off-by: Andy Lutomirski <luto@xxxxxxxxxxxxxx>
---
 arch/x86/include/asm/thread_info.h | 3 +--
 arch/x86/kernel/traps.c            | 4 ++--
 2 files changed, 3 insertions(+), 4 deletions(-)

diff --git a/arch/x86/include/asm/thread_info.h b/arch/x86/include/asm/thread_info.h
index 1d4e4f279a32..a2fa1899494e 100644
--- 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
index 42819886be0c..484eb03a3f32 100644
--- 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);
 }
-- 
2.1.0

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