x86/xen/smp_pv: Remove wait for CPU online

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>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Michael Kelley <mikelley@microsoft.com>
Tested-by: Oleksandr Natalenko <oleksandr@natalenko.name>
Tested-by: Helge Deller <deller@gmx.de> # parisc
Tested-by: Guilherme G. Piccoli <gpiccoli@igalia.com> # Steam Deck
Link: https://lore.kernel.org/r/20230512205256.369512093@linutronix.de

diff --git a/arch/x86/xen/smp_pv.c b/arch/x86/xen/smp_pv.c
index a6f9128..be40927 100644 (file)
--- 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 cpu, struct task_struct *idle)
 
        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;
 }