Commit 3a025de6 authored by Yi Sun's avatar Yi Sun Committed by Thomas Gleixner
Browse files

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: default avatarYi Sun <yi.y.sun@linux.intel.com>
Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
Reviewed-by: default avatarJuergen 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
parent f726c462

Documentation/admin-guide/kernel-parameters.txt

+5 −0
Original line number Diff line number Diff line
@@ -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

arch/x86/hyperv/Makefile

+4 −0
Original line number Diff line number Diff line 
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

arch/x86/hyperv/hv_spinlock.c

0 → 100644
+88 −0
Original line number Diff line number Diff line 
// 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);

arch/x86/include/asm/mshyperv.h

+2 −0
Original line number Diff line number Diff line
@@ -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

arch/x86/kernel/cpu/mshyperv.c

+14 −0
Original line number Diff line number Diff line
@@ -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

}

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