linux.git/include/linux/call_once.h, branch v6.14-rc2 Linux kernel source tree kvm: defer huge page recovery vhost task to later 2025-01-24T15:53:56+00:00 Keith Busch kbusch@kernel.org 2025-01-23T15:35:43+00:00 931656b9e2ff7029aee0b36e17780621948a6ac1 Some libraries want to ensure they are single threaded before forking, so making the kernel's kvm huge page recovery process a vhost task of the user process breaks those. The minijail library used by crosvm is one such affected application. Defer the task to after the first VM_RUN call, which occurs after the parent process has forked all its jailed processes. This needs to happen only once for the kvm instance, so introduce some general-purpose infrastructure for that, too. It's similar in concept to pthread_once; except it is actually usable, because the callback takes a parameter. Cc: Sean Christopherson <seanjc@google.com> Cc: Paolo Bonzini <pbonzini@redhat.com> Tested-by: Alyssa Ross <hi@alyssa.is> Signed-off-by: Keith Busch <kbusch@kernel.org> Message-ID: <20250123153543.2769928-1-kbusch@meta.com> [Move call_once API to include/linux. - Paolo] Cc: stable@vger.kernel.org Fixes: d96c77bd4eeb ("KVM: x86: switch hugepage recovery thread to vhost_task") Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> 
Some libraries want to ensure they are single threaded before forking,
so making the kernel's kvm huge page recovery process a vhost task of
the user process breaks those. The minijail library used by crosvm is
one such affected application.

Defer the task to after the first VM_RUN call, which occurs after the
parent process has forked all its jailed processes. This needs to happen
only once for the kvm instance, so introduce some general-purpose
infrastructure for that, too.  It's similar in concept to pthread_once;
except it is actually usable, because the callback takes a parameter.

Cc: Sean Christopherson <seanjc@google.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Tested-by: Alyssa Ross <hi@alyssa.is>
Signed-off-by: Keith Busch <kbusch@kernel.org>
Message-ID: <20250123153543.2769928-1-kbusch@meta.com>
[Move call_once API to include/linux. - Paolo]
Cc: stable@vger.kernel.org
Fixes: d96c77bd4eeb ("KVM: x86: switch hugepage recovery thread to vhost_task")
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>