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FAILED: patch "[PATCH] entry/kvm: Explicitly flush pending rcuog wakeup before last" failed to apply to 4.4-stable tree

PATCH [email protected] 1 participant 1 message Mar 1, 2021

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Stable branch x86 KVM x86 RCU
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The patch below does not apply to the 4.4-stable tree.
If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to <[email protected]>.

thanks,

greg k-h

------------------ original commit in Linus's tree ------------------

From 4ae7dc97f726ea95c58ac58af71cc034ad22d7de Mon Sep 17 00:00:00 2001
From: Frederic Weisbecker <[email protected]>
Date: Mon, 1 Feb 2021 00:05:48 +0100
Subject: [PATCH] entry/kvm: Explicitly flush pending rcuog wakeup before last
rescheduling point

Following the idle loop model, cleanly check for pending rcuog wakeup before the last rescheduling point upon resuming to guest mode. This way we can avoid to do it from rcu_user_enter() with the last resort self-IPI hack that enforces rescheduling.

Suggested-by Peter Zijlstra <[email protected]>
Signed-off-by Frederic Weisbecker <[email protected]>
Signed-off-by Peter Zijlstra (Intel) <[email protected]>
Signed-off-by Ingo Molnar <[email protected]>
Cc [email protected]
Link https://lkml.kernel.org/r/[email protected] open here
arch/x86/kvm/x86.c +1 -0
index 1b404e4d7dd8..b967c1c774a1 100644
@@ -1782,6 +1782,7 @@ EXPORT_SYMBOL_GPL(kvm_emulate_wrmsr);
 
 bool kvm_vcpu_exit_request(struct kvm_vcpu *vcpu)
 {
+	xfer_to_guest_mode_prepare();
 	return vcpu->mode == EXITING_GUEST_MODE || kvm_request_pending(vcpu) ||
 		xfer_to_guest_mode_work_pending();
 }
include/linux/entry-kvm.h +14 -0
index 9b93f8584ff7..8b2b1d68b954 100644
@@ -46,6 +46,20 @@ static inline int arch_xfer_to_guest_mode_handle_work(struct kvm_vcpu *vcpu,
  */
 int xfer_to_guest_mode_handle_work(struct kvm_vcpu *vcpu);
 
+/**
+ * xfer_to_guest_mode_prepare - Perform last minute preparation work that
+ *				need to be handled while IRQs are disabled
+ *				upon entering to guest.
+ *
+ * Has to be invoked with interrupts disabled before the last call
+ * to xfer_to_guest_mode_work_pending().
+ */
+static inline void xfer_to_guest_mode_prepare(void)
+{
+	lockdep_assert_irqs_disabled();
+	rcu_nocb_flush_deferred_wakeup();
+}
+
 /**
  * __xfer_to_guest_mode_work_pending - Check if work is pending
  *
kernel/rcu/tree.c +34 -10

70 lines not on this page · raw message

kernel/rcu/tree_plugin.h +1 -0
index 384856e4d13e..cdc1b7651c03 100644
@@ -2197,6 +2197,7 @@ void rcu_nocb_flush_deferred_wakeup(void)
 {
 	do_nocb_deferred_wakeup(this_cpu_ptr(&rcu_data));
 }
+EXPORT_SYMBOL_GPL(rcu_nocb_flush_deferred_wakeup);
 
 void __init rcu_init_nohz(void)
 {