KVM: fix race with level interrupts

When more than 1 source id is in use for the same GSI, we have the
following race related to handling irq_states race:

CPU 0 clears bit 0. CPU 0 read irq_state as 0. CPU 1 sets level to 1.
CPU 1 calls kvm_ioapic_set_irq(1). CPU 0 calls kvm_ioapic_set_irq(0).
Now ioapic thinks the level is 0 but irq_state is not 0.

Fix by performing all irq_states bitmap handling under pic/ioapic lock.
This also removes the need for atomics with irq_states handling.

Reported-by: Gleb Natapov <gleb@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>

1 files changed, 14 insertions, 1 deletions

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index a3e9409e90b6..2c75b400e40c 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -816,7 +816,20 @@ int kvm_read_guest_page_mmu(struct kvm_vcpu *vcpu, struct kvm_mmu *mmu,
 void kvm_propagate_fault(struct kvm_vcpu *vcpu, struct x86_exception *fault);
 bool kvm_require_cpl(struct kvm_vcpu *vcpu, int required_cpl);
 
-int kvm_pic_set_irq(void *opaque, int irq, int level);
+static inline int __kvm_irq_line_state(unsigned long *irq_state,
+                                       int irq_source_id, int level)
+{
+        /* Logical OR for level trig interrupt */
+        if (level)
+                __set_bit(irq_source_id, irq_state);
+        else
+                __clear_bit(irq_source_id, irq_state);
+
+        return !!(*irq_state);
+}
+
+int kvm_pic_set_irq(struct kvm_pic *pic, int irq, int irq_source_id, int level);
+void kvm_pic_clear_all(struct kvm_pic *pic, int irq_source_id);
 
 void kvm_inject_nmi(struct kvm_vcpu *vcpu);