This is a note to let you know that I've just added the patch titled
KVM: x86: ioapic: Fix level-triggered EOI and IOAPIC reconfigure race
to the 4.9-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git%3Ba=su...
The filename of the patch is: kvm-x86-ioapic-fix-level-triggered-eoi-and-ioapic-reconfigure-race.patch and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree, please let stable@vger.kernel.org know about it.
From foo@baz Thu Feb 1 13:58:04 CET 2018
From: Nikita Leshenko nikita.leshchenko@oracle.com Date: Sun, 5 Nov 2017 15:52:29 +0200 Subject: KVM: x86: ioapic: Fix level-triggered EOI and IOAPIC reconfigure race
From: Nikita Leshenko nikita.leshchenko@oracle.com
[ Upstream commit 0fc5a36dd6b345eb0d251a65c236e53bead3eef7 ]
KVM uses ioapic_handled_vectors to track vectors that need to notify the IOAPIC on EOI. The problem is that IOAPIC can be reconfigured while an interrupt with old configuration is pending or running and ioapic_handled_vectors only remembers the newest configuration; thus EOI from the old interrupt is not delievered to the IOAPIC.
A previous commit db2bdcbbbd32 ("KVM: x86: fix edge EOI and IOAPIC reconfig race") addressed this issue by adding pending edge-triggered interrupts to ioapic_handled_vectors, fixing this race for edge-triggered interrupts. The commit explicitly ignored level-triggered interrupts, but this race applies to them as well:
1) IOAPIC sends a level triggered interrupt vector to VCPU0 2) VCPU0's handler deasserts the irq line and reconfigures the IOAPIC to route the vector to VCPU1. The reconfiguration rewrites only the upper 32 bits of the IOREDTBLn register. (Causes KVM to update ioapic_handled_vectors for VCPU0 and it no longer includes the vector.) 3) VCPU0 sends EOI for the vector, but it's not delievered to the IOAPIC because the ioapic_handled_vectors doesn't include the vector. 4) New interrupts are not delievered to VCPU1 because remote_irr bit is set forever.
Therefore, the correct behavior is to add all pending and running interrupts to ioapic_handled_vectors.
This commit introduces a slight performance hit similar to commit db2bdcbbbd32 ("KVM: x86: fix edge EOI and IOAPIC reconfig race") for the rare case that the vector is reused by a non-IOAPIC source on VCPU0. We prefer to keep solution simple and not handle this case just as the original commit does.
Fixes: db2bdcbbbd32 ("KVM: x86: fix edge EOI and IOAPIC reconfig race")
Signed-off-by: Nikita Leshenko nikita.leshchenko@oracle.com Reviewed-by: Liran Alon liran.alon@oracle.com Signed-off-by: Konrad Rzeszutek Wilk konrad.wilk@oracle.com Signed-off-by: Radim Krčmář rkrcmar@redhat.com Signed-off-by: Sasha Levin alexander.levin@microsoft.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/kvm/ioapic.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-)
diff --git a/arch/x86/kvm/ioapic.c b/arch/x86/kvm/ioapic.c index 6e219e5c07d2..a7ac8688bba8 100644 --- a/arch/x86/kvm/ioapic.c +++ b/arch/x86/kvm/ioapic.c @@ -257,8 +257,7 @@ void kvm_ioapic_scan_entry(struct kvm_vcpu *vcpu, ulong *ioapic_handled_vectors) index == RTC_GSI) { if (kvm_apic_match_dest(vcpu, NULL, 0, e->fields.dest_id, e->fields.dest_mode) || - (e->fields.trig_mode == IOAPIC_EDGE_TRIG && - kvm_apic_pending_eoi(vcpu, e->fields.vector))) + kvm_apic_pending_eoi(vcpu, e->fields.vector)) __set_bit(e->fields.vector, ioapic_handled_vectors); }