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    Subject[PATCH 3.4-rc] KVM: VMX: Fix kvm_set_shared_msr() called in preemptible context
    Date
    kvm_set_shared_msr() may not be called in preemptible context,
    but vmx_set_msr() does so:

    BUG: using smp_processor_id() in preemptible [00000000] code: qemu-kvm/22713
    caller is kvm_set_shared_msr+0x32/0xa0 [kvm]
    Pid: 22713, comm: qemu-kvm Not tainted 3.4.0-rc3+ #39
    Call Trace:
    [<ffffffff8131fa82>] debug_smp_processor_id+0xe2/0x100
    [<ffffffffa0328ae2>] kvm_set_shared_msr+0x32/0xa0 [kvm]
    [<ffffffffa03a103b>] vmx_set_msr+0x28b/0x2d0 [kvm_intel]
    ...

    Making kvm_set_shared_msr() work in preemptible is cleaner, but
    it's used in the fast path. Making two variants is overkill, so
    this patch just disables preemption around the call.

    Reported-by: Dave Jones <davej@redhat.com>
    Signed-off-by: Avi Kivity <avi@redhat.com>
    ---
    arch/x86/kvm/vmx.c | 5 ++++-
    1 file changed, 4 insertions(+), 1 deletion(-)

    diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
    index ad85adf..4ff0ab9 100644
    --- a/arch/x86/kvm/vmx.c
    +++ b/arch/x86/kvm/vmx.c
    @@ -2210,9 +2210,12 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, u32 msr_index, u64 data)
    msr = find_msr_entry(vmx, msr_index);
    if (msr) {
    msr->data = data;
    - if (msr - vmx->guest_msrs < vmx->save_nmsrs)
    + if (msr - vmx->guest_msrs < vmx->save_nmsrs) {
    + preempt_disable();
    kvm_set_shared_msr(msr->index, msr->data,
    msr->mask);
    + preempt_enable();
    + }
    break;
    }
    ret = kvm_set_msr_common(vcpu, msr_index, data);
    --
    1.7.10


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