Dan,

On Wed, 30 May 2018, Mark Rutland wrote:

quoted

diff --git a/arch/x86/include/asm/barrier.h b/arch/x86/include/asm/barrier.h
index 042b5e892ed1..41f7435c84a7 100644
--- a/arch/x86/include/asm/barrier.h
+++ b/arch/x86/include/asm/barrier.h

@@ -38,10 +38,11 @@ static inline unsigned long array_index_mask_nospec(unsigned long index,
 {
 	unsigned long mask;
 
-	asm ("cmp %1,%2; sbb %0,%0;"
+	asm volatile ("cmp %1,%2; sbb %0,%0;"
 			:"=r" (mask)
 			:"g"(size),"r" (index)
 			:"cc");
+	barrier();
 	return mask;
 }

What does the barrier() prevent?

I don't think that inhibits the insertion of branches, and AFAIK the volatile
is sufficient to prevent elision of identical array_idx_nospec() calls.

I don't have an objection to it, regardless.

So long as the example is updated in the commit message, feel free to add:

Any update on this?

Thanks,

	tglx