KVM: x86: remove unnecessary memory barriers for shared MSRs

There is no smp_rmb matching the smp_wmb.  shared_msr_update is called from
hardware_enable, which in turn is called via on_each_cpu.  on_each_cpu
and must imply a read memory barrier (on x86 the rmb is achieved simply
through asm volatile in native_apic_mem_write).

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c675ea3351cfc854f786442d973ef5d36e1c0072..2d62229aac26c9b54ae141dd9926a8c720ad6ff3 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -222,11 +222,9 @@ static void shared_msr_update(unsigned slot, u32 msr)
 void kvm_define_shared_msr(unsigned slot, u32 msr)
 {
        BUG_ON(slot >= KVM_NR_SHARED_MSRS);
+       shared_msrs_global.msrs[slot] = msr;
        if (slot >= shared_msrs_global.nr)
                shared_msrs_global.nr = slot + 1;
-       shared_msrs_global.msrs[slot] = msr;
-       /* we need ensured the shared_msr_global have been updated */
-       smp_wmb();
 }
 EXPORT_SYMBOL_GPL(kvm_define_shared_msr);