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Commitf458d039db("kvm: ioapic: Lazy update IOAPIC EOI") introduces the following infinite loop: BUG: stack guard page was hit at 000000008f595917 \ (stack is 00000000bdefe5a4..00000000ae2b06f5) kernel stack overflow (double-fault): 0000 [#1] SMP NOPTI RIP: 0010:kvm_set_irq+0x51/0x160 [kvm] Call Trace: irqfd_resampler_ack+0x32/0x90 [kvm] kvm_notify_acked_irq+0x62/0xd0 [kvm] kvm_ioapic_update_eoi_one.isra.0+0x30/0x120 [kvm] ioapic_set_irq+0x20e/0x240 [kvm] kvm_ioapic_set_irq+0x5c/0x80 [kvm] kvm_set_irq+0xbb/0x160 [kvm] ? kvm_hv_set_sint+0x20/0x20 [kvm] irqfd_resampler_ack+0x32/0x90 [kvm] kvm_notify_acked_irq+0x62/0xd0 [kvm] kvm_ioapic_update_eoi_one.isra.0+0x30/0x120 [kvm] ioapic_set_irq+0x20e/0x240 [kvm] kvm_ioapic_set_irq+0x5c/0x80 [kvm] kvm_set_irq+0xbb/0x160 [kvm] ? kvm_hv_set_sint+0x20/0x20 [kvm] .... The re-entrancy happens because the irq state is the OR of the interrupt state and the resamplefd state. That is, we don't want to show the state as 0 until we've had a chance to set the resamplefd. But if the interrupt has _not_ gone low then ioapic_set_irq is invoked again, causing an infinite loop. This can only happen for a level-triggered interrupt, otherwise irqfd_inject would immediately set the KVM_USERSPACE_IRQ_SOURCE_ID high and then low. Fortunately, in the case of level-triggered interrupts the VMEXIT already happens because TMR is set. Thus, fix the bug by restricting the lazy invocation of the ack notifier to edge-triggered interrupts, the only ones that need it. Tested-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com> Reported-by: borisvk@bstnet.org Suggested-by: Paolo Bonzini <pbonzini@redhat.com> Link: https://www.spinics.net/lists/kvm/msg213512.html Fixes:f458d039db("kvm: ioapic: Lazy update IOAPIC EOI") Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=207489 Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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