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From:   Tianyu Lan <ltykernel@gmail.com>
To:     kys@microsoft.com, haiyangz@microsoft.com, sthemmin@microsoft.com,
        wei.liu@kernel.org, decui@microsoft.com, tglx@linutronix.de,
        mingo@redhat.com, bp@alien8.de, x86@kernel.org, hpa@zytor.com,
        michael.h.kelley@microsoft.com
Cc:     Tianyu Lan <Tianyu.Lan@microsoft.com>,
        linux-hyperv@vger.kernel.org, linux-kernel@vger.kernel.org,
        vkuznets@redhat.com
Subject: [PATCH] x86/Hyper-V: Initialize Hyper-V stimer after enabling lapic
Date:   Wed,  4 Aug 2021 14:48:43 -0400
Message-Id: <20210804184843.513524-1-ltykernel@gmail.com>
MIME-Version: 1.0
Content-Transfer-Encoding: 8bit
Precedence: bulk

From: Tianyu Lan <Tianyu.Lan@microsoft.com>

Hyper-V Isolation VM doesn't have PIT/HPET legacy timer and only
provide stimer. Initialize Hyper-v stimer just after enabling
lapic to avoid kernel stuck during calibrating TSC due to no
available timer.

Signed-off-by: Tianyu Lan <Tianyu.Lan@microsoft.com>
---
 arch/x86/hyperv/hv_init.c      | 29 -----------------------------
 arch/x86/kernel/cpu/mshyperv.c | 22 ++++++++++++++++++++++
 2 files changed, 22 insertions(+), 29 deletions(-)

diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index 6f247e7e07eb..4a643a85d570 100644
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c
@@ -271,25 +271,6 @@ static struct syscore_ops hv_syscore_ops = {
 	.resume		= hv_resume,
 };
 
-static void (* __initdata old_setup_percpu_clockev)(void);
-
-static void __init hv_stimer_setup_percpu_clockev(void)
-{
-	/*
-	 * Ignore any errors in setting up stimer clockevents
-	 * as we can run with the LAPIC timer as a fallback.
-	 */
-	(void)hv_stimer_alloc(false);
-
-	/*
-	 * Still register the LAPIC timer, because the direct-mode STIMER is
-	 * not supported by old versions of Hyper-V. This also allows users
-	 * to switch to LAPIC timer via /sys, if they want to.
-	 */
-	if (old_setup_percpu_clockev)
-		old_setup_percpu_clockev();
-}
-
 static void __init hv_get_partition_id(void)
 {
 	struct hv_get_partition_id *output_page;
@@ -396,16 +377,6 @@ void __init hyperv_init(void)
 		wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
 	}
 
-	/*
-	 * hyperv_init() is called before LAPIC is initialized: see
-	 * apic_intr_mode_init() -> x86_platform.apic_post_init() and
-	 * apic_bsp_setup() -> setup_local_APIC(). The direct-mode STIMER
-	 * depends on LAPIC, so hv_stimer_alloc() should be called from
-	 * x86_init.timers.setup_percpu_clockev.
-	 */
-	old_setup_percpu_clockev = x86_init.timers.setup_percpu_clockev;
-	x86_init.timers.setup_percpu_clockev = hv_stimer_setup_percpu_clockev;
-
 	hv_apic_init();
 
 	x86_init.pci.arch_init = hv_pci_init;
diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index 6b5835a087a3..dcfbd2770d7f 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -214,6 +214,20 @@ static void __init hv_smp_prepare_boot_cpu(void)
 #endif
 }
 
+static void (* __initdata old_setup_initr_mode)(void);
+
+static void __init hv_setup_initr_mode(void)
+{
+	if (old_setup_initr_mode)
+		old_setup_initr_mode();
+
+	/*
+	 * The direct-mode STIMER depends on LAPIC and so allocate
+	 * STIMER after calling initr node callback.
+	 */
+	(void)hv_stimer_alloc(false);
+}
+
 static void __init hv_smp_prepare_cpus(unsigned int max_cpus)
 {
 #ifdef CONFIG_X86_64
@@ -424,6 +438,7 @@ static void __init ms_hyperv_init_platform(void)
 	/* Register Hyper-V specific clocksource */
 	hv_init_clocksource();
 #endif
+
 	/*
 	 * TSC should be marked as unstable only after Hyper-V
 	 * clocksource has been initialized. This ensures that the
@@ -431,6 +446,13 @@ static void __init ms_hyperv_init_platform(void)
 	 */
 	if (!(ms_hyperv.features & HV_ACCESS_TSC_INVARIANT))
 		mark_tsc_unstable("running on Hyper-V");
+
+	/*
+	 * Override initr mode callback in order to allocate STIMER
+	 * after initalizing LAPIC.
+	 */
+	old_setup_initr_mode = x86_init.irqs.intr_mode_init;
+	x86_init.irqs.intr_mode_init = hv_setup_initr_mode;
 }
 
 static bool __init ms_hyperv_x2apic_available(void)
-- 
2.25.1