6.11-stable review patch. If anyone has any objections, please let me know.
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From: Paolo Bonzini pbonzini@redhat.com
commit d96c77bd4eeba469bddbbb14323d2191684da82a upstream.
kvm_vm_create_worker_thread() is meant to be used for kthreads that can consume significant amounts of CPU time on behalf of a VM or in response to how the VM behaves (for example how it accesses its memory). Therefore it wants to charge the CPU time consumed by that work to the VM's container.
However, because of these threads, cgroups which have kvm instances inside never complete freezing. This can be trivially reproduced:
root@test ~# mkdir /sys/fs/cgroup/test root@test ~# echo $$ > /sys/fs/cgroup/test/cgroup.procs root@test ~# qemu-system-x86_64 -nographic -enable-kvm
and in another terminal:
root@test ~# echo 1 > /sys/fs/cgroup/test/cgroup.freeze root@test ~# cat /sys/fs/cgroup/test/cgroup.events populated 1 frozen 0
The cgroup freezing happens in the signal delivery path but kvm_nx_huge_page_recovery_worker, while joining non-root cgroups, never calls into the signal delivery path and thus never gets frozen. Because the cgroup freezer determines whether a given cgroup is frozen by comparing the number of frozen threads to the total number of threads in the cgroup, the cgroup never becomes frozen and users waiting for the state transition may hang indefinitely.
Since the worker kthread is tied to a user process, it's better if it behaves similarly to user tasks as much as possible, including being able to send SIGSTOP and SIGCONT. In fact, vhost_task is all that kvm_vm_create_worker_thread() wanted to be and more: not only it inherits the userspace process's cgroups, it has other niceties like being parented properly in the process tree. Use it instead of the homegrown alternative.
Incidentally, the new code is also better behaved when you flip recovery back and forth to disabled and back to enabled. If your recovery period is 1 minute, it will run the next recovery after 1 minute independent of how many times you flipped the parameter.
(Commit message based on emails from Tejun).
Reported-by: Tejun Heo tj@kernel.org Reported-by: Luca Boccassi bluca@debian.org Acked-by: Tejun Heo tj@kernel.org Tested-by: Luca Boccassi bluca@debian.org Cc: stable@vger.kernel.org Reviewed-by: Sean Christopherson seanjc@google.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/include/asm/kvm_host.h | 4 + arch/x86/kvm/Kconfig | 1 arch/x86/kvm/mmu/mmu.c | 68 ++++++++++++-------------- include/linux/kvm_host.h | 6 -- virt/kvm/kvm_main.c | 103 ---------------------------------------- 5 files changed, 35 insertions(+), 147 deletions(-)
--- a/arch/x86/include/asm/kvm_host.h +++ b/arch/x86/include/asm/kvm_host.h @@ -26,6 +26,7 @@ #include <linux/irqbypass.h> #include <linux/hyperv.h> #include <linux/kfifo.h> +#include <linux/sched/vhost_task.h>
#include <asm/apic.h> #include <asm/pvclock-abi.h> @@ -1445,7 +1446,8 @@ struct kvm_arch { bool sgx_provisioning_allowed;
struct kvm_x86_pmu_event_filter __rcu *pmu_event_filter; - struct task_struct *nx_huge_page_recovery_thread; + struct vhost_task *nx_huge_page_recovery_thread; + u64 nx_huge_page_last;
#ifdef CONFIG_X86_64 /* The number of TDP MMU pages across all roots. */ --- a/arch/x86/kvm/Kconfig +++ b/arch/x86/kvm/Kconfig @@ -29,6 +29,7 @@ config KVM select HAVE_KVM_IRQ_BYPASS select HAVE_KVM_IRQ_ROUTING select HAVE_KVM_READONLY_MEM + select VHOST_TASK select KVM_ASYNC_PF select USER_RETURN_NOTIFIER select KVM_MMIO --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -7160,7 +7160,7 @@ static int set_nx_huge_pages(const char kvm_mmu_zap_all_fast(kvm); mutex_unlock(&kvm->slots_lock);
- wake_up_process(kvm->arch.nx_huge_page_recovery_thread); + vhost_task_wake(kvm->arch.nx_huge_page_recovery_thread); } mutex_unlock(&kvm_lock); } @@ -7306,7 +7306,7 @@ static int set_nx_huge_pages_recovery_pa mutex_lock(&kvm_lock);
list_for_each_entry(kvm, &vm_list, vm_list) - wake_up_process(kvm->arch.nx_huge_page_recovery_thread); + vhost_task_wake(kvm->arch.nx_huge_page_recovery_thread);
mutex_unlock(&kvm_lock); } @@ -7409,62 +7409,56 @@ static void kvm_recover_nx_huge_pages(st srcu_read_unlock(&kvm->srcu, rcu_idx); }
-static long get_nx_huge_page_recovery_timeout(u64 start_time) +static void kvm_nx_huge_page_recovery_worker_kill(void *data) { - bool enabled; - uint period; - - enabled = calc_nx_huge_pages_recovery_period(&period); - - return enabled ? start_time + msecs_to_jiffies(period) - get_jiffies_64() - : MAX_SCHEDULE_TIMEOUT; }
-static int kvm_nx_huge_page_recovery_worker(struct kvm *kvm, uintptr_t data) +static bool kvm_nx_huge_page_recovery_worker(void *data) { - u64 start_time; + struct kvm *kvm = data; + bool enabled; + uint period; long remaining_time;
- while (true) { - start_time = get_jiffies_64(); - remaining_time = get_nx_huge_page_recovery_timeout(start_time); - - set_current_state(TASK_INTERRUPTIBLE); - while (!kthread_should_stop() && remaining_time > 0) { - schedule_timeout(remaining_time); - remaining_time = get_nx_huge_page_recovery_timeout(start_time); - set_current_state(TASK_INTERRUPTIBLE); - } - - set_current_state(TASK_RUNNING); - - if (kthread_should_stop()) - return 0; + enabled = calc_nx_huge_pages_recovery_period(&period); + if (!enabled) + return false;
- kvm_recover_nx_huge_pages(kvm); + remaining_time = kvm->arch.nx_huge_page_last + msecs_to_jiffies(period) + - get_jiffies_64(); + if (remaining_time > 0) { + schedule_timeout(remaining_time); + /* check for signals and come back */ + return true; } + + __set_current_state(TASK_RUNNING); + kvm_recover_nx_huge_pages(kvm); + kvm->arch.nx_huge_page_last = get_jiffies_64(); + return true; }
int kvm_mmu_post_init_vm(struct kvm *kvm) { - int err; - if (nx_hugepage_mitigation_hard_disabled) return 0;
- err = kvm_vm_create_worker_thread(kvm, kvm_nx_huge_page_recovery_worker, 0, - "kvm-nx-lpage-recovery", - &kvm->arch.nx_huge_page_recovery_thread); - if (!err) - kthread_unpark(kvm->arch.nx_huge_page_recovery_thread); + kvm->arch.nx_huge_page_last = get_jiffies_64(); + kvm->arch.nx_huge_page_recovery_thread = vhost_task_create( + kvm_nx_huge_page_recovery_worker, kvm_nx_huge_page_recovery_worker_kill, + kvm, "kvm-nx-lpage-recovery");
- return err; + if (!kvm->arch.nx_huge_page_recovery_thread) + return -ENOMEM; + + vhost_task_start(kvm->arch.nx_huge_page_recovery_thread); + return 0; }
void kvm_mmu_pre_destroy_vm(struct kvm *kvm) { if (kvm->arch.nx_huge_page_recovery_thread) - kthread_stop(kvm->arch.nx_huge_page_recovery_thread); + vhost_task_stop(kvm->arch.nx_huge_page_recovery_thread); }
#ifdef CONFIG_KVM_GENERIC_MEMORY_ATTRIBUTES --- a/include/linux/kvm_host.h +++ b/include/linux/kvm_host.h @@ -2370,12 +2370,6 @@ static inline int kvm_arch_vcpu_run_pid_ } #endif /* CONFIG_HAVE_KVM_VCPU_RUN_PID_CHANGE */
-typedef int (*kvm_vm_thread_fn_t)(struct kvm *kvm, uintptr_t data); - -int kvm_vm_create_worker_thread(struct kvm *kvm, kvm_vm_thread_fn_t thread_fn, - uintptr_t data, const char *name, - struct task_struct **thread_ptr); - #ifdef CONFIG_KVM_XFER_TO_GUEST_WORK static inline void kvm_handle_signal_exit(struct kvm_vcpu *vcpu) { --- a/virt/kvm/kvm_main.c +++ b/virt/kvm/kvm_main.c @@ -6573,106 +6573,3 @@ void kvm_exit(void) kvm_irqfd_exit(); } EXPORT_SYMBOL_GPL(kvm_exit); - -struct kvm_vm_worker_thread_context { - struct kvm *kvm; - struct task_struct *parent; - struct completion init_done; - kvm_vm_thread_fn_t thread_fn; - uintptr_t data; - int err; -}; - -static int kvm_vm_worker_thread(void *context) -{ - /* - * The init_context is allocated on the stack of the parent thread, so - * we have to locally copy anything that is needed beyond initialization - */ - struct kvm_vm_worker_thread_context *init_context = context; - struct task_struct *parent; - struct kvm *kvm = init_context->kvm; - kvm_vm_thread_fn_t thread_fn = init_context->thread_fn; - uintptr_t data = init_context->data; - int err; - - err = kthread_park(current); - /* kthread_park(current) is never supposed to return an error */ - WARN_ON(err != 0); - if (err) - goto init_complete; - - err = cgroup_attach_task_all(init_context->parent, current); - if (err) { - kvm_err("%s: cgroup_attach_task_all failed with err %d\n", - __func__, err); - goto init_complete; - } - - set_user_nice(current, task_nice(init_context->parent)); - -init_complete: - init_context->err = err; - complete(&init_context->init_done); - init_context = NULL; - - if (err) - goto out; - - /* Wait to be woken up by the spawner before proceeding. */ - kthread_parkme(); - - if (!kthread_should_stop()) - err = thread_fn(kvm, data); - -out: - /* - * Move kthread back to its original cgroup to prevent it lingering in - * the cgroup of the VM process, after the latter finishes its - * execution. - * - * kthread_stop() waits on the 'exited' completion condition which is - * set in exit_mm(), via mm_release(), in do_exit(). However, the - * kthread is removed from the cgroup in the cgroup_exit() which is - * called after the exit_mm(). This causes the kthread_stop() to return - * before the kthread actually quits the cgroup. - */ - rcu_read_lock(); - parent = rcu_dereference(current->real_parent); - get_task_struct(parent); - rcu_read_unlock(); - cgroup_attach_task_all(parent, current); - put_task_struct(parent); - - return err; -} - -int kvm_vm_create_worker_thread(struct kvm *kvm, kvm_vm_thread_fn_t thread_fn, - uintptr_t data, const char *name, - struct task_struct **thread_ptr) -{ - struct kvm_vm_worker_thread_context init_context = {}; - struct task_struct *thread; - - *thread_ptr = NULL; - init_context.kvm = kvm; - init_context.parent = current; - init_context.thread_fn = thread_fn; - init_context.data = data; - init_completion(&init_context.init_done); - - thread = kthread_run(kvm_vm_worker_thread, &init_context, - "%s-%d", name, task_pid_nr(current)); - if (IS_ERR(thread)) - return PTR_ERR(thread); - - /* kthread_run is never supposed to return NULL */ - WARN_ON(thread == NULL); - - wait_for_completion(&init_context.init_done); - - if (!init_context.err) - *thread_ptr = thread; - - return init_context.err; -}