linux-kernel - [ 43/52] KVM: VMX: Fix kvm_set_shared_msr() called in preemptible context

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Message-Id: <20120510173136.631086068@linuxfoundation.org>
Date:	Thu, 10 May 2012 10:32:15 -0700
From:	Greg KH <gregkh@...uxfoundation.org>
To:	linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:	torvalds@...ux-foundation.org, akpm@...ux-foundation.org,
	alan@...rguk.ukuu.org.uk, Dave Jones <davej@...hat.com>,
	Avi Kivity <avi@...hat.com>,
	Marcelo Tosatti <mtosatti@...hat.com>
Subject: [ 43/52] KVM: VMX: Fix kvm_set_shared_msr() called in preemptible context

3.3-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Avi Kivity <avi@...hat.com>

(cherry picked from commit 2225fd56049643c1a7d645c0ce9d499d43c7974e)

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@...hat.com>
Signed-off-by: Avi Kivity <avi@...hat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@...hat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 arch/x86/kvm/vmx.c |    5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -2219,9 +2219,12 @@ static int vmx_set_msr(struct kvm_vcpu *
 		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);


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