x86/hyperv: Enable PV qspinlock for Hyper-V

Implement the required wait and kick callbacks to support PV spinlocks in
Hyper-V guests.

[ tglx: Document the requirement for disabling interrupts in the wait()
  	callback. Remove goto and unnecessary includes. Add prototype
	for hv_vcpu_is_preempted(). Adapted to pending paravirt changes. ]

Signed-off-by: Yi Sun <yi.y.sun@linux.intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Juergen Gross <jgross@suse.com>
Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Stephen Hemminger <sthemmin@microsoft.com>
Cc: Michael Kelley (EOSG) <Michael.H.Kelley@microsoft.com>
Cc: chao.p.peng@intel.com
Cc: chao.gao@intel.com
Cc: isaku.yamahata@intel.com
Cc: tianyu.lan@microsoft.com
Link: https://lkml.kernel.org/r/1538987374-51217-3-git-send-email-yi.y.sun@linux.intel.com

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 9871e649ffeffe8798cd20a1450377a4f4777fca..4cdf6a673592d3530e3eddf958fc84de5fd8c458 100644 (file)
--- 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 b21ee65c410183ea2492d5ee3403a6fcd91f4cd2..1c11f9420a820da28de24e6dab643b253b2915da 100644 (file)
--- 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 (file)
index 0000000..a861b04
--- /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 f37704497d8f352ff14230e29cd4527e67fb80ea..0d6271cce198dcd1ac0108ac9a4ea803a6e8b2dc 100644 (file)
--- 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 ad12733f605854b4eae755102d5b68060fdf4bb8..1c72f3819eb123d8fb7271a0c49cf94aceae5ee3 100644 (file)
--- 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
 }