[Xen-devel] [PATCH] xen: arm: clear the exclusive monitor on exception return

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

Otherwise context switching between two vcpus which are contending the same
lock can result in a spurious success.

This is not required on ARMv8 since eret implicitly clears the monitor.

Signed-off-by: Ian Campbell <ian.campbell@xxxxxxxxxx>
---
 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
 
 /*
-- 
1.7.2.5


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