memfd is not needed by layered products right now, but it's currently enabled in our package. Let's disable it in QEMU so it doesn't get exposed unecessarily and untested. This commit from libvirt gives us a good summary of what the feature is: (but this BZ is about disabling it in QEMU, which is enough) commit 24b74d187cab48a9dc9f409ea78900154c709579 Author: Marc-André Lureau <marcandre.lureau> Date: Thu Nov 15 15:55:53 2018 +0400 qemu: add memfd source type Add a new memoryBacking source type "memfd", supported by QEMU (when the capability is available). A memfd is a specialized anonymous memory kind. As such, an anonymous source type could be automatically using a memfd. However, there are some complications when migrating from different memory backends in qemu (mainly due to the internal object naming at this point, but there could be more). For now, it is simpler and safer to simply introduce a new source type "memfd". Eventually, the "anonymous" type could learn to use memfd transparently in a separate change. The main benefits are that it doesn't need to create filesystem files, and it also enforces sealing, providing a bit more safety.
QA_ACK, please?
Verify: qemu-kvm-4.1.0-4.module+el8.1.0+4020+16089f93 kernel-4.18.0-131.el8.x86_64 Object memory-backend-memfd is not supported now. # /usr/libexec/qemu-kvm -object memory-backend-memfd,id=mem0 qemu-kvm: -object memory-backend-memfd,id=mem0: invalid object type: memory-backend-memfd
Since the problem described in this bug report should be resolved in a recent advisory, it has been closed with a resolution of ERRATA. For information on the advisory, and where to find the updated files, follow the link below. If the solution does not work for you, open a new bug report. https://access.redhat.com/errata/RHBA-2019:3723
This is a bit unfortunate; it's a lot easier to work with memfd when you're doing vhost-user and just want to specify share=on