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charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit On 1/27/25 19:22, Keith Busch wrote: >> It's not clear to me that calling vhost_task_wake() before vhost_task_start() is >> allowed, which is why I deliberately waited until the task was started to make it >> visible. Though FWIW, doing "vhost_task_wake(nx_thread)" before vhost_task_start() >> doesn't explode. > > Hm, it does look questionable to try to wake a process that hadn't been > started yet, but I think it may be okay: task state will be TASK_NEW > before vhost_task_start(), which looks like will cause wake_up_process() > to do nothing. Yes, it's okay because both wake_up_new_task() and try_to_wake_up() take p->pi_lock. try_to_wake_up() does not match either bit in TASK_NORMAL (which is TASK_INTERRUPTIBLE | TASK_UNINTERRUPTIBLE) and does nothing. I'm queuing the patch with the store before vhost_task_start, and acquire/release instead of just READ_ONCE/WRITE_ONCE. diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 74c20dbb92da..6d5708146384 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -7127,7 +7127,8 @@ static void kvm_wake_nx_recovery_thread(struct kvm *kvm) * may not be valid even though the VM is globally visible. Do nothing, * as such a VM can't have any possible NX huge pages. */ - struct vhost_task *nx_thread = READ_ONCE(kvm->arch.nx_huge_page_recovery_thread); + struct vhost_task *nx_thread = + smp_load_acquire(&kvm->arch.nx_huge_page_recovery_thread); if (nx_thread) vhost_task_wake(nx_thread); @@ -7474,10 +7475,10 @@ static void kvm_mmu_start_lpage_recovery(struct once *once) if (!nx_thread) return; - vhost_task_start(nx_thread); + /* Make the task visible only once it is fully created. */ + smp_store_release(&kvm->arch.nx_huge_page_recovery_thread, nx_thread); - /* Make the task visible only once it is fully started. */ - WRITE_ONCE(kvm->arch.nx_huge_page_recovery_thread, nx_thread); + vhost_task_start(nx_thread); } int kvm_mmu_post_init_vm(struct kvm *kvm)