From: Mark Wood-Patrick <mwoodpatr...@nvidia.com>
Sent: Wednesday, July 1, 2020 11:26 AM
To: qemu-devel@nongnu.org
Cc: Mark Wood-Patrick <mwoodpatr...@nvidia.com>
Subject: Seeing a problem in multi cpu runs where memory mapped pcie device
register reads are returning incorrect values
Background
I have a test environment which runs QEMU 4.2 with a plugin that runs two
copies of a PCIE device simulator on a CentOS 7.5 host with an Ubuntu 18.04
guest. When running with a single QEMU CPU using:
-cpu kvm64,+lahf_lm -M q35,kernel-irqchip=off -device
intel-iommu,intremap=on
Our tests run fine. But when running with multiple cpu's:
-cpu kvm64,+lahf_lm -M q35,kernel-irqchip=off -device
intel-iommu,intremap=on -smp 2,sockets=1,cores=2
The values retuned are correct all the way up the call stack and in
KVM_EXIT_MMIO in kvm_cpu_exec (qemu-4.2.0/accel/kvm/kvm-all.c:2365) but the
value returned to the device driver which initiated the read is 0.
Question
Is anyone else running QEMU 4.2 in multi cpu mode? Is anyone getting incorrect
reads from memory mapped device registers when running in this mode? I would
appreciate any pointers on how best to debug the flow from KVM_EXIT_MMIO back
to the device driver running on the guest
