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Date:      Sat, 1 Mar 2014 03:17:59 +0000 (UTC)
From:      Neel Natu <neel@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r262646 - head/sys/amd64/vmm
Message-ID:  <201403010317.s213Hx74034996@svn.freebsd.org>
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Author: neel
Date: Sat Mar  1 03:17:58 2014
New Revision: 262646
URL: http://svnweb.freebsd.org/changeset/base/262646

Log:
  Fix a race between VMRUN() and vcpu_notify_event() due to 'vcpu->hostcpu'
  being updated outside of the vcpu_lock(). The race is benign and could
  potentially result in a missed notification about a pending interrupt to
  a vcpu. The interrupt would not be lost but rather delayed until the next
  VM exit.
  
  The vcpu's hostcpu is now updated concurrently with the vcpu state change.
  When the vcpu transitions to the RUNNING state the hostcpu is set to 'curcpu'.
  It is set to 'NOCPU' in all other cases.
  
  Reviewed by:	grehan

Modified:
  head/sys/amd64/vmm/vmm.c

Modified: head/sys/amd64/vmm/vmm.c
==============================================================================
--- head/sys/amd64/vmm/vmm.c	Sat Mar  1 03:17:46 2014	(r262645)
+++ head/sys/amd64/vmm/vmm.c	Sat Mar  1 03:17:58 2014	(r262646)
@@ -870,6 +870,14 @@ vcpu_set_state_locked(struct vcpu *vcpu,
 		    "vcpu idle state"));
 	}
 
+	if (vcpu->state == VCPU_RUNNING) {
+		KASSERT(vcpu->hostcpu == curcpu, ("curcpu %d and hostcpu %d "
+		    "mismatch for running vcpu", curcpu, vcpu->hostcpu));
+	} else {
+		KASSERT(vcpu->hostcpu == NOCPU, ("Invalid hostcpu %d for a "
+		    "vcpu that is not running", vcpu->hostcpu));
+	}
+
 	/*
 	 * The following state transitions are allowed:
 	 * IDLE -> FROZEN -> IDLE
@@ -894,6 +902,11 @@ vcpu_set_state_locked(struct vcpu *vcpu,
 		return (EBUSY);
 
 	vcpu->state = newstate;
+	if (newstate == VCPU_RUNNING)
+		vcpu->hostcpu = curcpu;
+	else
+		vcpu->hostcpu = NOCPU;
+
 	if (newstate == VCPU_IDLE)
 		wakeup(&vcpu->state);
 
@@ -1152,9 +1165,7 @@ restart:
 	restore_guest_fpustate(vcpu);
 
 	vcpu_require_state(vm, vcpuid, VCPU_RUNNING);
-	vcpu->hostcpu = curcpu;
 	error = VMRUN(vm->cookie, vcpuid, rip, pmap, &vm->rendezvous_func);
-	vcpu->hostcpu = NOCPU;
 	vcpu_require_state(vm, vcpuid, VCPU_FROZEN);
 
 	save_guest_fpustate(vcpu);
@@ -1548,19 +1559,28 @@ vcpu_notify_event(struct vm *vm, int vcp
 
 	vcpu_lock(vcpu);
 	hostcpu = vcpu->hostcpu;
-	if (hostcpu == NOCPU) {
-		if (vcpu->state == VCPU_SLEEPING)
-			wakeup_one(vcpu);
-	} else {
-		if (vcpu->state != VCPU_RUNNING)
-			panic("invalid vcpu state %d", vcpu->state);
+	if (vcpu->state == VCPU_RUNNING) {
+		KASSERT(hostcpu != NOCPU, ("vcpu running on invalid hostcpu"));
 		if (hostcpu != curcpu) {
-			if (lapic_intr)
+			if (lapic_intr) {
 				vlapic_post_intr(vcpu->vlapic, hostcpu,
 				    vmm_ipinum);
-			else
+			} else {
 				ipi_cpu(hostcpu, vmm_ipinum);
+			}
+		} else {
+			/*
+			 * If the 'vcpu' is running on 'curcpu' then it must
+			 * be sending a notification to itself (e.g. SELF_IPI).
+			 * The pending event will be picked up when the vcpu
+			 * transitions back to guest context.
+			 */
 		}
+	} else {
+		KASSERT(hostcpu == NOCPU, ("vcpu state %d not consistent "
+		    "with hostcpu %d", vcpu->state, hostcpu));
+		if (vcpu->state == VCPU_SLEEPING)
+			wakeup_one(vcpu);
 	}
 	vcpu_unlock(vcpu);
 }

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