6.12-stable review patch. If anyone has any objections, please let me know.
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From: Keith Busch kbusch@kernel.org
commit 916b7f42b3b3b539a71c204a9b49fdc4ca92cd82 upstream.
A VMM may send a non-fatal signal to its threads, including vCPU tasks, at any time, and thus may signal vCPU tasks during KVM_RUN. If a vCPU task receives the signal while its trying to spawn the huge page recovery vhost task, then KVM_RUN will fail due to copy_process() returning -ERESTARTNOINTR.
Rework call_once() to mark the call complete if and only if the called function succeeds, and plumb the function's true error code back to the call_once() invoker. This provides userspace with the correct, non-fatal error code so that the VMM doesn't terminate the VM on -ENOMEM, and allows subsequent KVM_RUN a succeed by virtue of retrying creation of the NX huge page task.
Co-developed-by: Sean Christopherson seanjc@google.com Signed-off-by: Sean Christopherson seanjc@google.com [implemented the kvm user side] Signed-off-by: Keith Busch kbusch@kernel.org Message-ID: 20250227230631.303431-3-kbusch@meta.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com Cc: Alistair Delva adelva@google.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/kvm/mmu/mmu.c | 10 ++++------ include/linux/call_once.h | 43 ++++++++++++++++++++++++++++++++----------- 2 files changed, 36 insertions(+), 17 deletions(-)
--- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -7578,7 +7578,7 @@ static bool kvm_nx_huge_page_recovery_wo return true; }
-static void kvm_mmu_start_lpage_recovery(struct once *once) +static int kvm_mmu_start_lpage_recovery(struct once *once) { struct kvm_arch *ka = container_of(once, struct kvm_arch, nx_once); struct kvm *kvm = container_of(ka, struct kvm, arch); @@ -7590,12 +7590,13 @@ static void kvm_mmu_start_lpage_recovery kvm, "kvm-nx-lpage-recovery");
if (IS_ERR(nx_thread)) - return; + return PTR_ERR(nx_thread);
vhost_task_start(nx_thread);
/* Make the task visible only once it is fully started. */ WRITE_ONCE(kvm->arch.nx_huge_page_recovery_thread, nx_thread); + return 0; }
int kvm_mmu_post_init_vm(struct kvm *kvm) @@ -7603,10 +7604,7 @@ int kvm_mmu_post_init_vm(struct kvm *kvm if (nx_hugepage_mitigation_hard_disabled) return 0;
- call_once(&kvm->arch.nx_once, kvm_mmu_start_lpage_recovery); - if (!kvm->arch.nx_huge_page_recovery_thread) - return -ENOMEM; - return 0; + return call_once(&kvm->arch.nx_once, kvm_mmu_start_lpage_recovery); }
void kvm_mmu_pre_destroy_vm(struct kvm *kvm) --- a/include/linux/call_once.h +++ b/include/linux/call_once.h @@ -26,20 +26,41 @@ do { \ __once_init((once), #once, &__key); \ } while (0)
-static inline void call_once(struct once *once, void (*cb)(struct once *)) +/* + * call_once - Ensure a function has been called exactly once + * + * @once: Tracking struct + * @cb: Function to be called + * + * If @once has never completed successfully before, call @cb and, if + * it returns a zero or positive value, mark @once as completed. Return + * the value returned by @cb + * + * If @once has completed succesfully before, return 0. + * + * The call to @cb is implicitly surrounded by a mutex, though for + * efficiency the * function avoids taking it after the first call. + */ +static inline int call_once(struct once *once, int (*cb)(struct once *)) { - /* Pairs with atomic_set_release() below. */ - if (atomic_read_acquire(&once->state) == ONCE_COMPLETED) - return; + int r, state;
- guard(mutex)(&once->lock); - WARN_ON(atomic_read(&once->state) == ONCE_RUNNING); - if (atomic_read(&once->state) != ONCE_NOT_STARTED) - return; + /* Pairs with atomic_set_release() below. */ + if (atomic_read_acquire(&once->state) == ONCE_COMPLETED) + return 0;
- atomic_set(&once->state, ONCE_RUNNING); - cb(once); - atomic_set_release(&once->state, ONCE_COMPLETED); + guard(mutex)(&once->lock); + state = atomic_read(&once->state); + if (unlikely(state != ONCE_NOT_STARTED)) + return WARN_ON_ONCE(state != ONCE_COMPLETED) ? -EINVAL : 0; + + atomic_set(&once->state, ONCE_RUNNING); + r = cb(once); + if (r < 0) + atomic_set(&once->state, ONCE_NOT_STARTED); + else + atomic_set_release(&once->state, ONCE_COMPLETED); + return r; }
#endif /* _LINUX_CALL_ONCE_H */