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From da707adaee9ff035c943178160be54a90de00cb3 Mon Sep 17 00:00:00 2001
From: Paolo Bonzini <pbonzini@redhat.com>
Date: Mon, 4 May 2020 12:19:45 -0400
Subject: [PATCH 2/3] kvm: ioapic: Restrict lazy EOI update to edge-triggered
interrupts
Commit f458d039db7e ("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: f458d039db7e ("kvm: ioapic: Lazy update IOAPIC EOI")
Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=207489
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/kvm/ioapic.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/arch/x86/kvm/ioapic.c b/arch/x86/kvm/ioapic.c
index 750ff0b29404..d057376bd3d3 100644
--- a/arch/x86/kvm/ioapic.c
+++ b/arch/x86/kvm/ioapic.c
@@ -225,12 +225,12 @@ static int ioapic_set_irq(struct kvm_ioapic *ioapic, unsigned int irq,
}
/*
- * AMD SVM AVIC accelerate EOI write and do not trap,
- * in-kernel IOAPIC will not be able to receive the EOI.
- * In this case, we do lazy update of the pending EOI when
- * trying to set IOAPIC irq.
+ * AMD SVM AVIC accelerate EOI write iff the interrupt is edge
+ * triggered, in which case the in-kernel IOAPIC will not be able
+ * to receive the EOI. In this case, we do a lazy update of the
+ * pending EOI when trying to set IOAPIC irq.
*/
- if (kvm_apicv_activated(ioapic->kvm))
+ if (edge && kvm_apicv_activated(ioapic->kvm))
ioapic_lazy_update_eoi(ioapic, irq);
/*
--
2.26.2
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