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authorDexuan Cui <decui@microsoft.com>2021-01-16 14:31:36 -0800
committerWei Liu <wei.liu@kernel.org>2021-01-17 15:20:50 +0000
commitfff7b5e6ee63c5d20406a131b260c619cdd24fd1 (patch)
treec6bc9955bb26af60222003cdde97a2b0eebd392b /arch
parentad0a6bad44758afa3b440c254a24999a0c7e35d5 (diff)
x86/hyperv: Initialize clockevents after LAPIC is initialized
With commit 4df4cb9e99f8, the Hyper-V direct-mode STIMER is actually initialized before LAPIC is initialized: see apic_intr_mode_init() x86_platform.apic_post_init() hyperv_init() hv_stimer_alloc() apic_bsp_setup() setup_local_APIC() setup_local_APIC() temporarily disables LAPIC, initializes it and re-eanble it. The direct-mode STIMER depends on LAPIC, and when it's registered, it can be programmed immediately and the timer can fire very soon: hv_stimer_init clockevents_config_and_register clockevents_register_device tick_check_new_device tick_setup_device tick_setup_periodic(), tick_setup_oneshot() clockevents_program_event When the timer fires in the hypervisor, if the LAPIC is in the disabled state, new versions of Hyper-V ignore the event and don't inject the timer interrupt into the VM, and hence the VM hangs when it boots. Note: when the VM starts/reboots, the LAPIC is pre-enabled by the firmware, so the window of LAPIC being temporarily disabled is pretty small, and the issue can only happen once out of 100~200 reboots for a 40-vCPU VM on one dev host, and on another host the issue doesn't reproduce after 2000 reboots. The issue is more noticeable for kdump/kexec, because the LAPIC is disabled by the first kernel, and stays disabled until the kdump/kexec kernel enables it. This is especially an issue to a Generation-2 VM (for which Hyper-V doesn't emulate the PIT timer) when CONFIG_HZ=1000 (rather than CONFIG_HZ=250) is used. Fix the issue by moving hv_stimer_alloc() to a later place where the LAPIC timer is initialized. Fixes: 4df4cb9e99f8 ("x86/hyperv: Initialize clockevents earlier in CPU onlining") Signed-off-by: Dexuan Cui <decui@microsoft.com> Reviewed-by: Michael Kelley <mikelley@microsoft.com> Link: https://lore.kernel.org/r/20210116223136.13892-1-decui@microsoft.com Signed-off-by: Wei Liu <wei.liu@kernel.org>
Diffstat (limited to 'arch')
-rw-r--r--arch/x86/hyperv/hv_init.c29
1 files changed, 26 insertions, 3 deletions
diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
index 4638a52d8eae..6375967a8244 100644
--- a/arch/x86/hyperv/hv_init.c
+++ b/arch/x86/hyperv/hv_init.c
@@ -315,6 +315,25 @@ 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();
+
+ /*
+ * 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();
+}
+
/*
* This function is to be invoked early in the boot sequence after the
* hypervisor has been detected.
@@ -393,10 +412,14 @@ void __init hyperv_init(void)
wrmsrl(HV_X64_MSR_HYPERCALL, hypercall_msr.as_uint64);
/*
- * Ignore any errors in setting up stimer clockevents
- * as we can run with the LAPIC timer as a fallback.
+ * 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.
*/
- (void)hv_stimer_alloc();
+ old_setup_percpu_clockev = x86_init.timers.setup_percpu_clockev;
+ x86_init.timers.setup_percpu_clockev = hv_stimer_setup_percpu_clockev;
hv_apic_init();