vhost_task: KVM: Fix a race where KVM wakes an exited task

[PATCH 0/3] vhost_task: KVM: Fix a race where KVM wakes an exited task

Posted by Sean Christopherson 1 month, 1 week ago

Fix a bug where KVM attempts to wake a vhost task that has already exited in
response to a fatal signal, and tack on a few cleanups to harden against
introducing similar bugs in the future.

Somehow, this only started causing problems when commit 56180dd20c19 ("futex:
Use RCU-based per-CPU reference counting instead of rcuref_t") landed.  I have
no idea why the futex changes exposed the bug, and I don't care all that much,
as this is firmly a KVM bug.

Sean Christopherson (3):
  vhost_task: KVM: Don't wake KVM x86's recovery thread if vhost task
    was killed
  vhost_task: Allow caller to omit handle_sigkill() callback
  KVM: x86/mmu: Don't register a sigkill callback for NX hugepage
    recovery tasks

 arch/x86/kvm/mmu/mmu.c           |  9 ++----
 include/linux/sched/vhost_task.h |  1 +
 kernel/vhost_task.c              | 52 +++++++++++++++++++++++++++++---
 3 files changed, 51 insertions(+), 11 deletions(-)


base-commit: 1b237f190eb3d36f52dffe07a40b5eb210280e00
-- 
2.51.0.261.g7ce5a0a67e-goog

Re: [PATCH 0/3] vhost_task: KVM: Fix a race where KVM wakes an exited task

Posted by Lei Yang 1 month ago

Tested this series of patches with vhost-net regression tests,
everything works fine.

Tested-by: Lei Yang <leiyang@redhat.com>

On Tue, Aug 26, 2025 at 8:40 AM Sean Christopherson <seanjc@google.com> wrote:
>
> Fix a bug where KVM attempts to wake a vhost task that has already exited in
> response to a fatal signal, and tack on a few cleanups to harden against
> introducing similar bugs in the future.
>
> Somehow, this only started causing problems when commit 56180dd20c19 ("futex:
> Use RCU-based per-CPU reference counting instead of rcuref_t") landed.  I have
> no idea why the futex changes exposed the bug, and I don't care all that much,
> as this is firmly a KVM bug.
>
> Sean Christopherson (3):
>   vhost_task: KVM: Don't wake KVM x86's recovery thread if vhost task
>     was killed
>   vhost_task: Allow caller to omit handle_sigkill() callback
>   KVM: x86/mmu: Don't register a sigkill callback for NX hugepage
>     recovery tasks
>
>  arch/x86/kvm/mmu/mmu.c           |  9 ++----
>  include/linux/sched/vhost_task.h |  1 +
>  kernel/vhost_task.c              | 52 +++++++++++++++++++++++++++++---
>  3 files changed, 51 insertions(+), 11 deletions(-)
>
>
> base-commit: 1b237f190eb3d36f52dffe07a40b5eb210280e00
> --
> 2.51.0.261.g7ce5a0a67e-goog
>
>