[Xen-devel] [PATCH 4/7] xen/mmu: BUG_ON when racing to swap middle leaf.

[Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>]

The initial bootup code uses set_phys_to_machine quite a lot, and after
bootup it would be used by the balloon driver. The balloon driver does have
mutex lock so this should not be necessary - but just in case, add
a BUG_ON if we do hit this scenario.

[v2: Change from WARN to BUG_ON]
Reviewed-by: Ian Campbell <Ian.Campbell@xxxxxxxxxxxxx>
Signed-off-by: Konrad Rzeszutek Wilk <konrad.wilk@xxxxxxxxxx>
---
 arch/x86/xen/mmu.c |    3 ++-
 1 files changed, 2 insertions(+), 1 deletions(-)

diff --git a/arch/x86/xen/mmu.c b/arch/x86/xen/mmu.c
index 6d5b49b..0cce0c2 100644
--- a/arch/x86/xen/mmu.c
+++ b/arch/x86/xen/mmu.c
@@ -613,7 +613,8 @@ bool __set_phys_to_machine(unsigned long pfn, unsigned long 
mfn)
 
                /* Swap over from MISSING to IDENTITY if needed. */
                if (p2m_top[topidx][mididx] == p2m_missing) {
-                       p2m_top[topidx][mididx] = p2m_identity;
+                       BUG_ON(cmpxchg(&p2m_top[topidx][mididx], p2m_missing,
+                               p2m_identity) != p2m_missing);
                        return true;
                }
        }
-- 
1.7.1


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