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KVM: x86: remove unnecessary memory barriers for shared MSRs

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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>
This commit is contained in:
Paolo Bonzini 2015-07-29 11:06:34 +02:00
parent d71ba78834
commit c847fe8895
1 changed files with 1 additions and 3 deletions
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4
arch/x86/kvm/x86.c
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@ -222,11 +222,9 @@ static void shared_msr_update(unsigned slot, u32 msr)
void kvm_define_shared_msr(unsigned slot, u32 msr) void kvm_define_shared_msr(unsigned slot, u32 msr)
{ {
BUG_ON(slot >= KVM_NR_SHARED_MSRS); BUG_ON(slot >= KVM_NR_SHARED_MSRS);
shared_msrs_global.msrs[slot] = msr;
if (slot >= shared_msrs_global.nr) if (slot >= shared_msrs_global.nr)
shared_msrs_global.nr = slot + 1; 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); EXPORT_SYMBOL_GPL(kvm_define_shared_msr);