[tip: smp/core] x86/xen/smp_pv: Remove wait for CPU online

[tip-bot2 for Thomas Gleixner]

The following commit has been merged into the smp/core branch of tip:

Commit-ID:     2de7fd26d90729c4e3430f9924b199dea810a9bc
Gitweb:        https://git.kernel.org/tip/2de7fd26d90729c4e3430f9924b199dea810a9bc
Author:        Thomas Gleixner <tglx@xxxxxxxxxxxxx>
AuthorDate:    Fri, 12 May 2023 23:07:24 +02:00
Committer:     Peter Zijlstra <peterz@xxxxxxxxxxxxx>
CommitterDate: Mon, 15 May 2023 13:44:54 +02:00

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@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Tested-by: Michael Kelley <mikelley@xxxxxxxxxxxxx>
Tested-by: Oleksandr Natalenko <oleksandr@xxxxxxxxxxxxxx>
Tested-by: Helge Deller <deller@xxxxxx> # parisc
Tested-by: Guilherme G. Piccoli <gpiccoli@xxxxxxxxxx> # Steam Deck
Link: https://lore.kernel.org/r/20230512205256.369512093@xxxxxxxxxxxxx
---
 arch/x86/xen/smp_pv.c | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/arch/x86/xen/smp_pv.c b/arch/x86/xen/smp_pv.c
index a6f9128..be40927 100644
--- 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;
 }