[Xen-changelog] [xen master] xen: arm: clear the exclusive monitor on exception return

[patchbot@xxxxxxx]

commit c57c50c1de759583d5de629fec205254280da4f0
Author:     Ian Campbell <ian.campbell@xxxxxxxxxx>
AuthorDate: Wed Jul 17 12:18:51 2013 +0100
Commit:     Ian Campbell <ian.campbell@xxxxxxxxxx>
CommitDate: Fri Jul 19 14:50:04 2013 +0100

    xen: arm: clear the exclusive monitor on exception return
    
    Otherwise context switching between two vcpus which are contending the same
    lock can result in a spurious success.
    
    Our spinlock and atomics code (which we get from Linux) rely on this 
behaviour
    because they use non-exclusive stores for single instruction operations 
(e.g.
    spin_unlock or atomic_set).
    
    This is not required on ARMv8 since eret implicitly clears the monitor.
    
    Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
    Acked-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
    Acked-by: Tim Deegan <tim@xxxxxxx>
---
 xen/arch/arm/arm32/entry.S |    1 +
 1 files changed, 1 insertions(+), 0 deletions(-)

diff --git a/xen/arch/arm/arm32/entry.S b/xen/arch/arm/arm32/entry.S
index 76814dd..1c26835 100644
--- a/xen/arch/arm/arm32/entry.S
+++ b/xen/arch/arm/arm32/entry.S
@@ -117,6 +117,7 @@ ENTRY(return_to_hypervisor)
         msr SPSR_hyp, r11
         pop {r0-r12}
         add sp, #(UREGS_SP_usr - UREGS_sp); /* SP, LR, SPSR, PC */
+        clrex
         eret
 
 /*
--
generated by git-patchbot for /home/xen/git/xen.git#master

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