x86/xen/p2m: Replace ACCESS_ONCE with READ_ONCE

ACCESS_ONCE does not work reliably on non-scalar types. For
example gcc 4.6 and 4.7 might remove the volatile tag for such
accesses during the SRA (scalar replacement of aggregates) step
(https://gcc.gnu.org/bugzilla/show_bug.cgi?id=58145)

Change the p2m code to replace ACCESS_ONCE with READ_ONCE.

Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Acked-by: David Vrabel <david.vrabel@citrix.com>

diff --git a/arch/x86/xen/p2m.c b/arch/x86/xen/p2m.c
index edbc7a63fd737f0ca13edac752e1f06341f9dd97..cb7101692a753515ecd501358f5617ba38baec1b 100644 (file)
--- a/arch/x86/xen/p2m.c
+++ b/arch/x86/xen/p2m.c
@@ -554,7 +554,7 @@ static bool alloc_p2m(unsigned long pfn)
                mid_mfn = NULL;
        }
 
-       p2m_pfn = pte_pfn(ACCESS_ONCE(*ptep));
+       p2m_pfn = pte_pfn(READ_ONCE(*ptep));
        if (p2m_pfn == PFN_DOWN(__pa(p2m_identity)) ||
            p2m_pfn == PFN_DOWN(__pa(p2m_missing))) {
                /* p2m leaf page is missing */