[PATCH 39/42] KVM: SVM: Move INTR vmexit out of atomic code

Avi Kivity
2009-11-16T12:27:11Z

From: Joerg Roedel <joerg.roedel@amd.com>

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>
---
arch/x86/kvm/svm.c | 26 +++++++++++++++++++++++++-
1 files changed, 25 insertions(+), 1 deletions(-)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index e372854..884bffc 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];
--
1.6.5.2