diff mbox series

[PATCHv3,2/2] kvm: retry nx_huge_page_recovery_thread creation

Message ID 20250227230631.303431-3-kbusch@meta.com (mailing list archive)
State New, archived
Headers show
Series [PATCHv3,1/2] vhost: return task creation error instead of NULL | expand

Commit Message

Keith Busch Feb. 27, 2025, 11:06 p.m. UTC 
From: Sean Christopherson <seanjc@google.com>

A VMM may send a signal to its threads while they've entered KVM_RUN. If
that thread happens to be trying to make the huge page recovery vhost
task, then it fails with -ERESTARTNOINTR. We need to retry if that
happens, so call_once needs to be retryable. Make call_once complete
only if what it called was successful.

[implemented the kvm user side]
Signed-off-by: Keith Busch <kbusch@kernel.org>
---
 arch/x86/kvm/mmu/mmu.c    | 10 ++++------
 include/linux/call_once.h | 16 +++++++++++-----
 2 files changed, 15 insertions(+), 11 deletions(-)

Comments

Simon Horman March 4, 2025, 3:59 p.m. UTC | #1 
On Thu, Feb 27, 2025 at 03:06:31PM -0800, Keith Busch wrote:
> From: Sean Christopherson <seanjc@google.com>
> 
> A VMM may send a signal to its threads while they've entered KVM_RUN. If
> that thread happens to be trying to make the huge page recovery vhost
> task, then it fails with -ERESTARTNOINTR. We need to retry if that
> happens, so call_once needs to be retryable. Make call_once complete
> only if what it called was successful.
> 
> [implemented the kvm user side]
> Signed-off-by: Keith Busch <kbusch@kernel.org>

...

> diff --git a/include/linux/call_once.h b/include/linux/call_once.h
> index 6261aa0b3fb00..ddcfd91493eaa 100644
> --- a/include/linux/call_once.h
> +++ b/include/linux/call_once.h
> @@ -26,20 +26,26 @@ do {									\
>  	__once_init((once), #once, &__key);				\
>  } while (0)
>  
> -static inline void call_once(struct once *once, void (*cb)(struct once *))
> +static inline int call_once(struct once *once, int (*cb)(struct once *))
>  {
> +	int r;
> +
>          /* Pairs with atomic_set_release() below.  */
>          if (atomic_read_acquire(&once->state) == ONCE_COMPLETED)
> -                return;
> +		return 0;
>  
>          guard(mutex)(&once->lock);
>          WARN_ON(atomic_read(&once->state) == ONCE_RUNNING);
>          if (atomic_read(&once->state) != ONCE_NOT_STARTED)
> -                return;
> +                return -EINVAL;

Hi Keith,

A minor nit from my side:

As you are changing this line, and it seems like there will be another
revision of this series anyway, please consider updating the indentation to
use tabs.

>  
>          atomic_set(&once->state, ONCE_RUNNING);
> -        cb(once);
> -        atomic_set_release(&once->state, ONCE_COMPLETED);
> +	r = cb(once);
> +	if (r)
> +		atomic_set(&once->state, ONCE_NOT_STARTED);
> +	else
> +		atomic_set_release(&once->state, ONCE_COMPLETED);
> +	return r;
>  }
>  
>  #endif /* _LINUX_CALL_ONCE_H */
> -- 
> 2.43.5
> 
>
Keith Busch March 4, 2025, 4:07 p.m. UTC | #2 
On Tue, Mar 04, 2025 at 03:59:22PM +0000, Simon Horman wrote:
> A minor nit from my side:
> 
> As you are changing this line, and it seems like there will be another
> revision of this series anyway, please consider updating the indentation to
> use tabs.

The patch is already applied to upstream and stable, and I think Paolo
must have taken care of the formatting because it looks good in the
commit now:

  https://web.git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=916b7f42b3b3b539a71c204a9b49fdc4ca92cd82
diff mbox series

Patch

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 18ca1ea6dc240..8160870398b90 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -7460,7 +7460,7 @@  static bool kvm_nx_huge_page_recovery_worker(void *data)
 	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);
@@ -7472,12 +7472,13 @@  static void kvm_mmu_start_lpage_recovery(struct once *once)
 				      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)
@@ -7485,10 +7486,7 @@  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)
diff --git a/include/linux/call_once.h b/include/linux/call_once.h
index 6261aa0b3fb00..ddcfd91493eaa 100644
--- a/include/linux/call_once.h
+++ b/include/linux/call_once.h
@@ -26,20 +26,26 @@  do {									\
 	__once_init((once), #once, &__key);				\
 } while (0)
 
-static inline void call_once(struct once *once, void (*cb)(struct once *))
+static inline int call_once(struct once *once, int (*cb)(struct once *))
 {
+	int r;
+
         /* Pairs with atomic_set_release() below.  */
         if (atomic_read_acquire(&once->state) == ONCE_COMPLETED)
-                return;
+		return 0;
 
         guard(mutex)(&once->lock);
         WARN_ON(atomic_read(&once->state) == ONCE_RUNNING);
         if (atomic_read(&once->state) != ONCE_NOT_STARTED)
-                return;
+                return -EINVAL;
 
         atomic_set(&once->state, ONCE_RUNNING);
-        cb(once);
-        atomic_set_release(&once->state, ONCE_COMPLETED);
+	r = cb(once);
+	if (r)
+		atomic_set(&once->state, ONCE_NOT_STARTED);
+	else
+		atomic_set_release(&once->state, ONCE_COMPLETED);
+	return r;
 }
 
 #endif /* _LINUX_CALL_ONCE_H */