From: dv <dv@openbsd.org>
Date: Tue, 11 May 2021 22:04:10 +0000 (+0000)
Subject: vmm(4): fix flawed physical cpu tracking logic in svm_run_vcpu
X-Git-Url: http://artulab.com/gitweb/?a=commitdiff_plain;h=97ad4f7f93830151ea04ac20ee6bfaaea2593cb4;p=openbsd

vmm(4): fix flawed physical cpu tracking logic in svm_run_vcpu

Replace the overly complicated logic used to track which CPU we are on
in svm_run_vcpu. This fixes an issue where ltr causes a #GP on exit in
certain conditions due to referencing the wrong GDT.

This was primarily witnessed with NixOS guests that performed a heavy
amount of disk io.

Reported by Josh Rickmar. Tested by Josh & abieber@. OK mlarkin@.
---

diff --git a/sys/arch/amd64/amd64/vmm.c b/sys/arch/amd64/amd64/vmm.c
index ebf2bce6b36..b1c49b057d4 100644
--- a/sys/arch/amd64/amd64/vmm.c
+++ b/sys/arch/amd64/amd64/vmm.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: vmm.c,v 1.280 2021/04/06 00:19:58 dv Exp $	*/
+/*	$OpenBSD: vmm.c,v 1.281 2021/05/11 22:04:10 dv Exp $	*/
 /*
  * Copyright (c) 2014 Mike Larkin <mlarkin@openbsd.org>
  *
@@ -6970,15 +6970,14 @@ vmm_handle_cpuid(struct vcpu *vcpu)
 int
 vcpu_run_svm(struct vcpu *vcpu, struct vm_run_params *vrp)
 {
-	int ret = 0, resume;
+	int ret = 0;
 	struct region_descriptor gdt;
-	struct cpu_info *ci;
+	struct cpu_info *ci = NULL;
 	uint64_t exit_reason;
 	struct schedstate_percpu *spc;
 	uint16_t irq;
 	struct vmcb *vmcb = (struct vmcb *)vcpu->vc_control_va;
 
-	resume = 0;
 	irq = vrp->vrp_irq;
 
 	/*
@@ -7000,7 +6999,7 @@ vcpu_run_svm(struct vcpu *vcpu, struct vm_run_params *vrp)
 
 	while (ret == 0) {
 		vmm_update_pvclock(vcpu);
-		if (!resume) {
+		if (ci != curcpu()) {
 			/*
 			 * We are launching for the first time, or we are
 			 * resuming from a different pcpu, so we need to
@@ -7106,8 +7105,6 @@ vcpu_run_svm(struct vcpu *vcpu, struct vm_run_params *vrp)
 
 		/* If we exited successfully ... */
 		if (ret == 0) {
-			resume = 1;
-
 			vcpu->vc_gueststate.vg_rflags = vmcb->v_rflags;
 
 			/*
@@ -7149,7 +7146,6 @@ vcpu_run_svm(struct vcpu *vcpu, struct vm_run_params *vrp)
 			/* Check if we should yield - don't hog the cpu */
 			spc = &ci->ci_schedstate;
 			if (spc->spc_schedflags & SPCF_SHOULDYIELD) {
-				resume = 0;
 				yield();
 			}
 		}