From 6d17a018d09801a2b18133a4febd81433bb0cf85 Mon Sep 17 00:00:00 2001 From: David Gibson Date: Thu, 15 Sep 2016 16:11:48 +1000 Subject: [PATCH] vfio/pci: Fix regression in MSI routing configuration d1f6af6 "kvm-irqchip: simplify kvm_irqchip_add_msi_route" was a cleanup of kvmchip routing configuration, that was mostly intended for x86. However, it also contains a subtle change in behaviour which breaks EEH[1] error recovery on certain VFIO passthrough devices on spapr guests. So far it's only been seen on a BCM5719 NIC on a POWER8 server, but there may be other hardware with the same problem. It's also possible there could be circumstances where it causes a bug on x86 as well, though I don't know of any obvious candidates. Prior to d1f6af6, both vfio_msix_vector_do_use() and vfio_add_kvm_msi_virq() used msg == NULL as a special flag to mark this as the "dummy" vector used to make the host hardware state sync with the guest expected hardware state in terms of MSI configuration. Specifically that flag caused vfio_add_kvm_msi_virq() to become a no-op, meaning the dummy irq would always be delivered via qemu. d1f6af6 changed vfio_add_kvm_msi_virq() so it takes a vector number instead of the msg parameter, and determines the correct message itself. The test for !msg was removed, and not replaced with anything there or in the caller. With an spapr guest which has a VFIO device, if an EEH error occurs on the host hardware, then the device will be isolated then reset. This is a combination of host and guest action, mediated by some EEH related hypercalls. I haven't fully traced the mechanics, but somehow installing the kvm irqchip route for the dummy irq on the BCM5719 means that after EEH reset and recovery, at least some irqs are no longer delivered to the guest. In particular, the guest never gets the link up event, and so the NIC is effectively dead. [1] EEH (Enhanced Error Handling) is an IBM POWER server specific PCI-* error reporting and recovery mechanism. The concept is somewhat similar to PCI-E AER, but the details are different. Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=1373802 Cc: Alex Williamson Cc: Peter Xu Cc: Gavin Shan Signed-off-by: David Gibson Cc: qemu-stable@nongnu.org Fixes: d1f6af6a17a6 ("kvm-irqchip: simplify kvm_irqchip_add_msi_route") Signed-off-by: Alex Williamson --- hw/vfio/pci.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-) diff --git a/hw/vfio/pci.c b/hw/vfio/pci.c index 7bfa17ce38..a5a620a0c4 100644 --- a/hw/vfio/pci.c +++ b/hw/vfio/pci.c @@ -496,7 +496,9 @@ static int vfio_msix_vector_do_use(PCIDevice *pdev, unsigned int nr, vfio_update_kvm_msi_virq(vector, *msg, pdev); } } else { - vfio_add_kvm_msi_virq(vdev, vector, nr, true); + if (msg) { + vfio_add_kvm_msi_virq(vdev, vector, nr, true); + } } /*