KVM: SVM: Move INTR vmexit out of atomic code

The nested SVM code emulates a #vmexit caused by a request
to open the irq window right in the request function. This
is a bug because the request function runs with preemption
and interrupts disabled but the #vmexit emulation might
sleep. This can cause a schedule()-while-atomic bug and is
fixed with this patch.

Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 25 insertions, 1 deletions

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index e37285446cb7..884bffc70c7f 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -85,6 +85,9 @@ struct nested_state {
         /* gpa pointers to the real vectors */
         u64 vmcb_msrpm;
 
+        /* A VMEXIT is required but not yet emulated */
+        bool exit_required;
+
         /* cache for intercepts of the guest */
         u16 intercept_cr_read;
         u16 intercept_cr_write;
@@ -1379,7 +1382,14 @@ static inline int nested_svm_intr(struct vcpu_svm *svm)
 
         svm->vmcb->control.exit_code = SVM_EXIT_INTR;
 
-        if (nested_svm_exit_handled(svm)) {
+        if (svm->nested.intercept & 1ULL) {
+                /*
+                 * The #vmexit can't be emulated here directly because this
+                 * code path runs with irqs and preemtion disabled. A
+                 * #vmexit emulation might sleep. Only signal request for
+                 * the #vmexit here.
+                 */
+                svm->nested.exit_required = true;
                 nsvm_printk("VMexit -> INTR\n");
                 return 1;
         }
@@ -2340,6 +2350,13 @@ static int handle_exit(struct kvm_vcpu *vcpu)
 
         trace_kvm_exit(exit_code, svm->vmcb->save.rip);
 
+        if (unlikely(svm->nested.exit_required)) {
+                nested_svm_vmexit(svm);
+                svm->nested.exit_required = false;
+
+                return 1;
+        }
+
         if (is_nested(svm)) {
                 int vmexit;
 
@@ -2615,6 +2632,13 @@ static void svm_vcpu_run(struct kvm_vcpu *vcpu)
         u16 gs_selector;
         u16 ldt_selector;
 
+        /*
+         * A vmexit emulation is required before the vcpu can be executed
+         * again.
+         */
+        if (unlikely(svm->nested.exit_required))
+                return;
+
         svm->vmcb->save.rax = vcpu->arch.regs[VCPU_REGS_RAX];
         svm->vmcb->save.rsp = vcpu->arch.regs[VCPU_REGS_RSP];
         svm->vmcb->save.rip = vcpu->arch.regs[VCPU_REGS_RIP];