[PATCH 3.4-rc] KVM: VMX: Fix kvm_set_shared_msr() called in preemptible context

From: Avi Kivity
Date: Wed Apr 18 2012 - 08:03:08 EST

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@xxxxxxxxxx>
Signed-off-by: Avi Kivity <avi@xxxxxxxxxx>
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,
+ preempt_enable();
+ }
ret = kvm_set_msr_common(vcpu, msr_index, data);

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