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From:   Thomas Gleixner <tglx@linutronix.de>
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Subject: [patch V4 17/37] x86/xen/smp_pv: Remove wait for CPU online
References: <20230512203426.452963764@linutronix.de>
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Date:   Fri, 12 May 2023 23:07:24 +0200 (CEST)
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From: Thomas Gleixner <tglx@linutronix.de>

Now that the core code drops sparse_irq_lock after the idle thread
synchronized, it's pointless to wait for the AP to mark itself online.

Whether the control CPU runs in a wait loop or sleeps in the core code
waiting for the online operation to complete makes no difference.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Michael Kelley <mikelley@microsoft.com>
---
 arch/x86/xen/smp_pv.c |   10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)


--- a/arch/x86/xen/smp_pv.c
+++ b/arch/x86/xen/smp_pv.c
@@ -340,11 +340,11 @@ static int xen_pv_cpu_up(unsigned int cp
 
 	xen_pmu_init(cpu);
 
-	rc = HYPERVISOR_vcpu_op(VCPUOP_up, xen_vcpu_nr(cpu), NULL);
-	BUG_ON(rc);
-
-	while (cpu_report_state(cpu) != CPU_ONLINE)
-		HYPERVISOR_sched_op(SCHEDOP_yield, NULL);
+	/*
+	 * Why is this a BUG? If the hypercall fails then everything can be
+	 * rolled back, no?
+	 */
+	BUG_ON(HYPERVISOR_vcpu_op(VCPUOP_up, xen_vcpu_nr(cpu), NULL));
 
 	return 0;
 }