On Fri, Feb 01, 2019 at 07:40:36PM -0200, Daniel Henrique Barboza wrote:
Update: I've figured it out.
The bug here was that, even running as root, I was getting errors like:
error : virQEMUCapsNewForBinaryInternal:4687 : internal error: Failed to probe QEMU binary with QMP: libvirt: error : prctl failed to enable 'dac_override' in the AMBIENT set: Operation not permitted
The reason is that the host has libcap-ng installed. ./configure uses it if available, setting WITH_CAPNG in the code. I am unsure if this has something to do with the libcap-ng configuration in this system I'm using or if there is something missing in the Libvirt code, but the spawned QEMU process isn't inheriting the capabilities it should have.
Disabling support of this lib with "--with-capng=no" in autogen.sh and rebuilding Libvirt fixed the problem. I was even able to see more NUMA nodes than I was before using the system libvirt (which is the original bug I am/was investigating).
Thanks!
Hey Daniel, I had the same problem with Mellanox RDMA device as backend for pvrdma device where the mlx5 driver also enforces CAP_IPC_LOCK. So at first i use this as a workaround but i knew that it is not a final approach as it makes a wrong use of memory. <memoryBacking> <locked/> </memoryBacking> Anyways, your tip helps so wanted to say thanks! Yuval
On 2/1/19 4:04 PM, Daniel Henrique Barboza wrote:
Hi,
I'm facing a strange behavior when running Libvirt from source code, latest upstream, on an Ubuntu 18.04.1 LTS Power 9 server. My QEMU guest - which is using VFIO and GPU passthrough - breaks on boot when trying to allocate a DMA window inside KVM.
Debugging the code, I've found out that the problem is related to the process not having CAP_IPC_LOCK - at least from the host kernel perspective.
This is strange because:
- the same VM running directly from QEMU command line works - the same VM running in the system Libvirt (v4.0.0, Ubuntu version) also works
What am I missing? My understanding on Linux process is that a process running as root should inherit the same capabilities of the user, which includes CAP_IPC_LOCK. Running Libvirt from source code should grant ipc_lock to it ... right?
Any help is appreciated. I can provide more details (VM XML for example) if necessary.
Thanks!
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