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

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Message-ID: <168422819921.404.10642421522981044037.tip-bot2@tip-bot2>
Date:   Tue, 16 May 2023 09:09:59 -0000
From:   "tip-bot2 for Thomas Gleixner" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Michael Kelley <mikelley@...rosoft.com>,
        Oleksandr Natalenko <oleksandr@...alenko.name>,
        Helge Deller <deller@....de>,
        "Guilherme G. Piccoli" <gpiccoli@...lia.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: smp/core] x86/xen/smp_pv: Remove wait for CPU online

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@...utronix.de>
AuthorDate:    Fri, 12 May 2023 23:07:24 +02:00
Committer:     Peter Zijlstra <peterz@...radead.org>
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@...utronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Tested-by: Michael Kelley <mikelley@...rosoft.com>
Tested-by: Oleksandr Natalenko <oleksandr@...alenko.name>
Tested-by: Helge Deller <deller@....de> # parisc
Tested-by: Guilherme G. Piccoli <gpiccoli@...lia.com> # Steam Deck
Link: https://lore.kernel.org/r/20230512205256.369512093@linutronix.de
---
 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;
 }