5 files changed, 113 insertions, 0 deletions

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 9871e649ffef..4cdf6a673592 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1385,6 +1385,11 @@
         hvc_iucv_allow= [S390]  Comma-separated list of z/VM user IDs.
                                 If specified, z/VM IUCV HVC accepts connections
                                 from listed z/VM user IDs only.
+
+        hv_nopvspin     [X86,HYPER_V] Disables the paravirt spinlock optimizations
+                                      which allow the hypervisor to 'idle' the
+                                      guest on lock contention.
+
         keep_bootcon    [KNL]
                         Do not unregister boot console at start. This is only
                         useful for debugging when something happens in the window
diff --git a/arch/x86/hyperv/Makefile b/arch/x86/hyperv/Makefile
index b21ee65c4101..1c11f9420a82 100644
--- a/arch/x86/hyperv/Makefile
+++ b/arch/x86/hyperv/Makefile
@@ -1,2 +1,6 @@
 obj-y                   := hv_init.o mmu.o nested.o
 obj-$(CONFIG_X86_64)    += hv_apic.o
+
+ifdef CONFIG_X86_64
+obj-$(CONFIG_PARAVIRT_SPINLOCKS)        += hv_spinlock.o
+endif
diff --git a/arch/x86/hyperv/hv_spinlock.c b/arch/x86/hyperv/hv_spinlock.c
new file mode 100644
index 000000000000..a861b0456b1a
--- /dev/null
+++ b/arch/x86/hyperv/hv_spinlock.c
@@ -0,0 +1,88 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Hyper-V specific spinlock code.
+ *
+ * Copyright (C) 2018, Intel, Inc.
+ *
+ * Author : Yi Sun <yi.y.sun@intel.com>
+ */
+
+#define pr_fmt(fmt) "Hyper-V: " fmt
+
+#include <linux/spinlock.h>
+
+#include <asm/mshyperv.h>
+#include <asm/paravirt.h>
+#include <asm/apic.h>
+
+static bool __initdata hv_pvspin = true;
+
+static void hv_qlock_kick(int cpu)
+{
+        apic->send_IPI(cpu, X86_PLATFORM_IPI_VECTOR);
+}
+
+static void hv_qlock_wait(u8 *byte, u8 val)
+{
+        unsigned long msr_val;
+        unsigned long flags;
+
+        if (in_nmi())
+                return;
+
+        /*
+         * Reading HV_X64_MSR_GUEST_IDLE MSR tells the hypervisor that the
+         * vCPU can be put into 'idle' state. This 'idle' state is
+         * terminated by an IPI, usually from hv_qlock_kick(), even if
+         * interrupts are disabled on the vCPU.
+         *
+         * To prevent a race against the unlock path it is required to
+         * disable interrupts before accessing the HV_X64_MSR_GUEST_IDLE
+         * MSR. Otherwise, if the IPI from hv_qlock_kick() arrives between
+         * the lock value check and the rdmsrl() then the vCPU might be put
+         * into 'idle' state by the hypervisor and kept in that state for
+         * an unspecified amount of time.
+         */
+        local_irq_save(flags);
+        /*
+         * Only issue the rdmsrl() when the lock state has not changed.
+         */
+        if (READ_ONCE(*byte) == val)
+                rdmsrl(HV_X64_MSR_GUEST_IDLE, msr_val);
+        local_irq_restore(flags);
+}
+
+/*
+ * Hyper-V does not support this so far.
+ */
+bool hv_vcpu_is_preempted(int vcpu)
+{
+        return false;
+}
+PV_CALLEE_SAVE_REGS_THUNK(hv_vcpu_is_preempted);
+
+void __init hv_init_spinlocks(void)
+{
+        if (!hv_pvspin || !apic ||
+            !(ms_hyperv.hints & HV_X64_CLUSTER_IPI_RECOMMENDED) ||
+            !(ms_hyperv.features & HV_X64_MSR_GUEST_IDLE_AVAILABLE)) {
+                pr_info("PV spinlocks disabled\n");
+                return;
+        }
+        pr_info("PV spinlocks enabled\n");
+
+        __pv_init_lock_hash();
+        pv_ops.lock.queued_spin_lock_slowpath = __pv_queued_spin_lock_slowpath;
+        pv_ops.lock.queued_spin_unlock = PV_CALLEE_SAVE(__pv_queued_spin_unlock);
+        pv_ops.lock.wait = hv_qlock_wait;
+        pv_ops.lock.kick = hv_qlock_kick;
+        pv_ops.lock.vcpu_is_preempted = PV_CALLEE_SAVE(hv_vcpu_is_preempted);
+}
+
+static __init int hv_parse_nopvspin(char *arg)
+{
+        hv_pvspin = false;
+        return 0;
+}
+early_param("hv_nopvspin", hv_parse_nopvspin);
diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
index f37704497d8f..0d6271cce198 100644
--- a/arch/x86/include/asm/mshyperv.h
+++ b/arch/x86/include/asm/mshyperv.h
@@ -351,6 +351,8 @@ int hyperv_flush_guest_mapping(u64 as);
 
 #ifdef CONFIG_X86_64
 void hv_apic_init(void);
+void __init hv_init_spinlocks(void);
+bool hv_vcpu_is_preempted(int vcpu);
 #else
 static inline void hv_apic_init(void) {}
 #endif
diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c
index ad12733f6058..1c72f3819eb1 100644
--- a/arch/x86/kernel/cpu/mshyperv.c
+++ b/arch/x86/kernel/cpu/mshyperv.c
@@ -199,6 +199,16 @@ static unsigned long hv_get_tsc_khz(void)
         return freq / 1000;
 }
 
+#if defined(CONFIG_SMP) && IS_ENABLED(CONFIG_HYPERV)
+static void __init hv_smp_prepare_boot_cpu(void)
+{
+        native_smp_prepare_boot_cpu();
+#if defined(CONFIG_X86_64) && defined(CONFIG_PARAVIRT_SPINLOCKS)
+        hv_init_spinlocks();
+#endif
+}
+#endif
+
 static void __init ms_hyperv_init_platform(void)
 {
         int hv_host_info_eax;
@@ -303,6 +313,10 @@ static void __init ms_hyperv_init_platform(void)
         if (ms_hyperv.misc_features & HV_STIMER_DIRECT_MODE_AVAILABLE)
                 alloc_intr_gate(HYPERV_STIMER0_VECTOR,
                                 hv_stimer0_callback_vector);
+
+# ifdef CONFIG_SMP
+        smp_ops.smp_prepare_boot_cpu = hv_smp_prepare_boot_cpu;
+# endif
 #endif
 }