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    Subject[PATCH 3.19 175/175] x86/xen/p2m: Replace ACCESS_ONCE with READ_ONCE
    Date
    3.19-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Christian Borntraeger <borntraeger@de.ibm.com>

    commit 1760f1eb7ec485197bd3a8a9c13e4160bb740275 upstream.

    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>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    arch/x86/xen/p2m.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    --- 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 */



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