Re: [libvirt PATCH] qemu: Add support for /dev/userfaultfd
On Thu, Feb 08, 2024 at 04:30:38PM +0100, Jiri Denemark wrote:
/dev/userfaultfd device is preferred over userfaultfd syscall for
post-copy migrations. Unless qemu driver is configured to disable mount
namespace or to forbid access to /dev/userfaultfd in cgroup_device_acl,
we will copy it to the limited /dev filesystem QEMU will have access to
and label it appropriately. So in the default configuration post-copy
migration will be allowed even without enabling
vm.unprivileged_userfaultfd sysctl.
Signed-off-by: Jiri Denemark <jdenemar(a)redhat.com>
---
Notes:
The question is what should we do with the
src/qemu/postcopy-migration.sysctl file which is installed by
libvirt.spec to /usr/lib/sysctl.d/60-qemu-postcopy-migration.conf by
default. The file is now useless and should ideally be removed, but only
when the host kernel is new enough to support /dev/userfaultfd
Just provide a meson_options.txt entry to disable it, and leave
it to be a distro problem to turn off in whatever releases they
consider new enough to prefer userfaultfd.
With regards,
Daniel
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