From 916b7f42b3b3b539a71c204a9b49fdc4ca92cd82 Mon Sep 17 00:00:00 2001 From: Keith Busch Date: Thu, 27 Feb 2025 15:06:31 -0800 Subject: kvm: retry nx_huge_page_recovery_thread creation 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 Signed-off-by: Sean Christopherson [implemented the kvm user side] Signed-off-by: Keith Busch Message-ID: <20250227230631.303431-3-kbusch@meta.com> Signed-off-by: Paolo Bonzini --- include/linux/call_once.h | 47 ++++++++++++++++++++++++++++++++++------------- 1 file changed, 34 insertions(+), 13 deletions(-) (limited to 'include') diff --git a/include/linux/call_once.h b/include/linux/call_once.h index 6261aa0b3fb0..13cd6469e7e5 100644 --- 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; - - guard(mutex)(&once->lock); - WARN_ON(atomic_read(&once->state) == ONCE_RUNNING); - if (atomic_read(&once->state) != ONCE_NOT_STARTED) - return; - - atomic_set(&once->state, ONCE_RUNNING); - cb(once); - atomic_set_release(&once->state, ONCE_COMPLETED); + int r, state; + + /* Pairs with atomic_set_release() below. */ + if (atomic_read_acquire(&once->state) == ONCE_COMPLETED) + return 0; + + 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 */ -- cgit v1.2.3