[PATCH v2 0/3] Add a unified parameter "nopvspin"

[PATCH v2 0/3] Add a unified parameter "nopvspin"

[Zhenzhong Duan]

There are cases folks want to disable spinlock optimization for
debug/test purpose. Xen and hyperv already have parameters "xen_nopvspin"
and "hv_nopvspin" to support that, but kvm doesn't.

The first patch adds that feature to KVM guest with "nopvspin".

For compatibility reason original parameters "xen_nopvspin" and
"hv_nopvspin" are retained and marked obsolete.

v2:
PATCH1: pick the print code change into seperate PATCH2,
        updated patch description             [Vitaly Kuznetsov]
PATCH2: new patch with print code change      [Vitaly Kuznetsov]
PATCH3: add Reviewed-by                       [Juergen Gross]

Thanks
Zhenzhong

[PATCH v2 1/4] x86/kvm: Add "nopvspin" parameter to disable PV spinlocks

[Zhenzhong Duan]

There are cases where a guest tries to switch spinlocks to bare metal
behavior (e.g. by setting "xen_nopvspin" on XEN platform and
"hv_nopvspin" on HYPER_V).

That feature is missed on KVM, add a new parameter "nopvspin" to disable
PV spinlocks for KVM guest.

This new parameter is also used to replace "xen_nopvspin" and
"hv_nopvspin".

The global variable pvspin isn't defined as __initdata as it's used at
runtime by XEN guest.

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krcmar <rkrcmar@redhat.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Wanpeng Li <wanpengli@tencent.com>
Cc: Jim Mattson <jmattson@google.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will@kernel.org>
---
 Documentation/admin-guide/kernel-parameters.txt | 4 ++++
 arch/x86/include/asm/qspinlock.h                | 1 +
 arch/x86/kernel/kvm.c                           | 7 +++++++
 kernel/locking/qspinlock.c                      | 7 +++++++
 4 files changed, 19 insertions(+)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index c7ac2f3..4b956d8 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5330,6 +5330,10 @@
 			as generic guest with no PV drivers. Currently support
 			XEN HVM, KVM, HYPER_V and VMWARE guest.
 
+	nopvspin	[X86,KVM] Disables the qspinlock slow path
+			using PV optimizations which allow the hypervisor to
+			'idle' the guest on lock contention.
+
 	xirc2ps_cs=	[NET,PCMCIA]
 			Format:
 			<irq>,<irq_mask>,<io>,<full_duplex>,<do_sound>,<lockup_hack>[,<irq2>[,<irq3>[,<irq4>]]]
diff --git a/arch/x86/include/asm/qspinlock.h b/arch/x86/include/asm/qspinlock.h
index 444d6fd..34a4484 100644
--- a/arch/x86/include/asm/qspinlock.h
+++ b/arch/x86/include/asm/qspinlock.h
@@ -32,6 +32,7 @@ static __always_inline u32 queued_fetch_set_pending_acquire(struct qspinlock *lo
 extern void __pv_init_lock_hash(void);
 extern void __pv_queued_spin_lock_slowpath(struct qspinlock *lock, u32 val);
 extern void __raw_callee_save___pv_queued_spin_unlock(struct qspinlock *lock);
+extern bool pvspin;
 
 #define	queued_spin_unlock queued_spin_unlock
 /**
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index e820568..a4f108d 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -842,6 +842,13 @@ void __init kvm_spinlock_init(void)
 	if (num_possible_cpus() == 1)
 		return;
 
+	if (!pvspin) {
+		pr_info("PV spinlocks disabled\n");
+		static_branch_disable(&virt_spin_lock_key);
+		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 =
diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c
index 2473f10..945b510 100644
--- a/kernel/locking/qspinlock.c
+++ b/kernel/locking/qspinlock.c
@@ -580,4 +580,11 @@ void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
 #include "qspinlock_paravirt.h"
 #include "qspinlock.c"
 
+bool pvspin = true;
+static __init int parse_nopvspin(char *arg)
+{
+	pvspin = false;
+	return 0;
+}
+early_param("nopvspin", parse_nopvspin);
 #endif
-- 
1.8.3.1

[PATCH v2 2/4] x86/kvm: Change print code to use pr_*() format

[Zhenzhong Duan]

pr_*() is preferred than printk(KERN_* ...), after change all the print
in arch/x86/kernel/kvm.c will have "KVM: xxx" style.

No functional change.

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krcmar <rkrcmar@redhat.com>
Cc: Sean Christopherson <sean.j.christopherson@intel.com>
Cc: Vitaly Kuznetsov <vkuznets@redhat.com>
Cc: Wanpeng Li <wanpengli@tencent.com>
Cc: Jim Mattson <jmattson@google.com>
Cc: Joerg Roedel <joro@8bytes.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
---
 arch/x86/kernel/kvm.c | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index a4f108d..7b8cf0d 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -7,6 +7,8 @@
  *   Authors: Anthony Liguori <aliguori@us.ibm.com>
  */
 
+#define pr_fmt(fmt) "KVM: " fmt
+
 #include <linux/context_tracking.h>
 #include <linux/init.h>
 #include <linux/kernel.h>
@@ -286,7 +288,7 @@ static void kvm_register_steal_time(void)
 		return;
 
 	wrmsrl(MSR_KVM_STEAL_TIME, (slow_virt_to_phys(st) | KVM_MSR_ENABLED));
-	pr_info("kvm-stealtime: cpu %d, msr %llx\n",
+	pr_info("stealtime: cpu %d, msr %llx\n",
 		cpu, (unsigned long long) slow_virt_to_phys(st));
 }
 
@@ -321,7 +323,7 @@ static void kvm_guest_cpu_init(void)
 
 		wrmsrl(MSR_KVM_ASYNC_PF_EN, pa);
 		__this_cpu_write(apf_reason.enabled, 1);
-		printk(KERN_INFO"KVM setup async PF for cpu %d\n",
+		pr_info("setup async PF for cpu %d\n",
 		       smp_processor_id());
 	}
 
@@ -347,7 +349,7 @@ static void kvm_pv_disable_apf(void)
 	wrmsrl(MSR_KVM_ASYNC_PF_EN, 0);
 	__this_cpu_write(apf_reason.enabled, 0);
 
-	printk(KERN_INFO"Unregister pv shared memory for cpu %d\n",
+	pr_info("Unregister pv shared memory for cpu %d\n",
 	       smp_processor_id());
 }
 
@@ -509,7 +511,7 @@ static void kvm_setup_pv_ipi(void)
 {
 	apic->send_IPI_mask = kvm_send_ipi_mask;
 	apic->send_IPI_mask_allbutself = kvm_send_ipi_mask_allbutself;
-	pr_info("KVM setup pv IPIs\n");
+	pr_info("setup pv IPIs\n");
 }
 
 static void kvm_smp_send_call_func_ipi(const struct cpumask *mask)
@@ -639,11 +641,11 @@ static void __init kvm_guest_init(void)
 	    !kvm_para_has_hint(KVM_HINTS_REALTIME) &&
 	    kvm_para_has_feature(KVM_FEATURE_STEAL_TIME)) {
 		smp_ops.send_call_func_ipi = kvm_smp_send_call_func_ipi;
-		pr_info("KVM setup pv sched yield\n");
+		pr_info("setup pv sched yield\n");
 	}
 	if (cpuhp_setup_state_nocalls(CPUHP_AP_ONLINE_DYN, "x86/kvm:online",
 				      kvm_cpu_online, kvm_cpu_down_prepare) < 0)
-		pr_err("kvm_guest: Failed to install cpu hotplug callbacks\n");
+		pr_err("failed to install cpu hotplug callbacks\n");
 #else
 	sev_map_percpu_data();
 	kvm_guest_cpu_init();
@@ -746,7 +748,7 @@ static __init int kvm_setup_pv_tlb_flush(void)
 			zalloc_cpumask_var_node(per_cpu_ptr(&__pv_tlb_mask, cpu),
 				GFP_KERNEL, cpu_to_node(cpu));
 		}
-		pr_info("KVM setup pv remote TLB flush\n");
+		pr_info("setup pv remote TLB flush\n");
 	}
 
 	return 0;
@@ -879,8 +881,8 @@ static void kvm_enable_host_haltpoll(void *i)
 void arch_haltpoll_enable(unsigned int cpu)
 {
 	if (!kvm_para_has_feature(KVM_FEATURE_POLL_CONTROL)) {
-		pr_err_once("kvm: host does not support poll control\n");
-		pr_err_once("kvm: host upgrade recommended\n");
+		pr_err_once("host does not support poll control\n");
+		pr_err_once("host upgrade recommended\n");
 		return;
 	}
 
-- 
1.8.3.1

[PATCH v2 3/4] xen: Mark "xen_nopvspin" parameter obsolete and map it to "nopvspin"

[Zhenzhong Duan]

Fix stale description of "xen_nopvspin" as we use qspinlock now.

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: Juergen Gross <jgross@suse.com>
Cc: Stefano Stabellini <sstabellini@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
---
 Documentation/admin-guide/kernel-parameters.txt |  7 ++++---
 arch/x86/xen/spinlock.c                         | 13 +++++++------
 2 files changed, 11 insertions(+), 9 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 4b956d8..1f0a62f 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -5303,8 +5303,9 @@
 			never -- do not unplug even if version check succeeds
 
 	xen_nopvspin	[X86,XEN]
-			Disables the ticketlock slowpath using Xen PV
-			optimizations.
+			Disables the qspinlock slowpath using Xen PV optimizations.
+			This parameter is obsoleted by "nopvspin" parameter, which
+			has equivalent effect for XEN platform.
 
 	xen_nopv	[X86]
 			Disables the PV optimizations forcing the HVM guest to
@@ -5330,7 +5331,7 @@
 			as generic guest with no PV drivers. Currently support
 			XEN HVM, KVM, HYPER_V and VMWARE guest.
 
-	nopvspin	[X86,KVM] Disables the qspinlock slow path
+	nopvspin	[X86,XEN,KVM] Disables the qspinlock slow path
 			using PV optimizations which allow the hypervisor to
 			'idle' the guest on lock contention.
 
diff --git a/arch/x86/xen/spinlock.c b/arch/x86/xen/spinlock.c
index 6deb490..092a53f 100644
--- a/arch/x86/xen/spinlock.c
+++ b/arch/x86/xen/spinlock.c
@@ -18,7 +18,6 @@
 static DEFINE_PER_CPU(int, lock_kicker_irq) = -1;
 static DEFINE_PER_CPU(char *, irq_name);
 static DEFINE_PER_CPU(atomic_t, xen_qlock_wait_nest);
-static bool xen_pvspin = true;
 
 static void xen_qlock_kick(int cpu)
 {
@@ -68,7 +67,7 @@ void xen_init_lock_cpu(int cpu)
 	int irq;
 	char *name;
 
-	if (!xen_pvspin)
+	if (!pvspin)
 		return;
 
 	WARN(per_cpu(lock_kicker_irq, cpu) >= 0, "spinlock on CPU%d exists on IRQ%d!\n",
@@ -93,7 +92,7 @@ void xen_init_lock_cpu(int cpu)
 
 void xen_uninit_lock_cpu(int cpu)
 {
-	if (!xen_pvspin)
+	if (!pvspin)
 		return;
 
 	unbind_from_irqhandler(per_cpu(lock_kicker_irq, cpu), NULL);
@@ -117,9 +116,9 @@ void __init xen_init_spinlocks(void)
 
 	/*  Don't need to use pvqspinlock code if there is only 1 vCPU. */
 	if (num_possible_cpus() == 1)
-		xen_pvspin = false;
+		pvspin = false;
 
-	if (!xen_pvspin) {
+	if (!pvspin) {
 		printk(KERN_DEBUG "xen: PV spinlocks disabled\n");
 		static_branch_disable(&virt_spin_lock_key);
 		return;
@@ -137,7 +136,9 @@ void __init xen_init_spinlocks(void)
 
 static __init int xen_parse_nopvspin(char *arg)
 {
-	xen_pvspin = false;
+	pr_notice("\"xen_nopvspin\" is deprecated, please use \"nopvspin\" instead\n");
+	if (xen_domain())
+		pvspin = false;
 	return 0;
 }
 early_param("xen_nopvspin", xen_parse_nopvspin);
-- 
1.8.3.1

[PATCH v2 4/4] x86/hyperv: Mark "hv_nopvspin" parameter obsolete and map it to "nopvspin"

[Zhenzhong Duan]

Includes asm/hypervisor.h in order to reference x86_hyper_type.

Signed-off-by: Zhenzhong Duan <zhenzhong.duan@oracle.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: "K. Y. Srinivasan" <kys@microsoft.com>
Cc: Haiyang Zhang <haiyangz@microsoft.com>
Cc: Stephen Hemminger <sthemmin@microsoft.com>
Cc: Sasha Levin <sashal@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: "H. Peter Anvin" <hpa@zytor.com>
---
 Documentation/admin-guide/kernel-parameters.txt | 6 +++++-
 arch/x86/hyperv/hv_spinlock.c                   | 9 +++++----
 2 files changed, 10 insertions(+), 5 deletions(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 1f0a62f..43f922c 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1436,6 +1436,10 @@
 	hv_nopvspin	[X86,HYPER_V] Disables the paravirt spinlock optimizations
 				      which allow the hypervisor to 'idle' the
 				      guest on lock contention.
+				      This parameter is obsoleted by "nopvspin"
+				      parameter, which has equivalent effect for
+				      HYPER_V platform.
+
 
 	keep_bootcon	[KNL]
 			Do not unregister boot console at start. This is only
@@ -5331,7 +5335,7 @@
 			as generic guest with no PV drivers. Currently support
 			XEN HVM, KVM, HYPER_V and VMWARE guest.
 
-	nopvspin	[X86,XEN,KVM] Disables the qspinlock slow path
+	nopvspin	[X86,XEN,KVM,HYPER_V] Disables the qspinlock slow path
 			using PV optimizations which allow the hypervisor to
 			'idle' the guest on lock contention.
 
diff --git a/arch/x86/hyperv/hv_spinlock.c b/arch/x86/hyperv/hv_spinlock.c
index 07f21a0..e00e319 100644
--- a/arch/x86/hyperv/hv_spinlock.c
+++ b/arch/x86/hyperv/hv_spinlock.c
@@ -12,12 +12,11 @@
 
 #include <linux/spinlock.h>
 
+#include <asm/hypervisor.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);
@@ -64,7 +63,7 @@ __visible bool hv_vcpu_is_preempted(int vcpu)
 
 void __init hv_init_spinlocks(void)
 {
-	if (!hv_pvspin || !apic ||
+	if (!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");
@@ -82,7 +81,9 @@ void __init hv_init_spinlocks(void)
 
 static __init int hv_parse_nopvspin(char *arg)
 {
-	hv_pvspin = false;
+	pr_notice("\"hv_nopvspin\" is deprecated, please use \"nopvspin\" instead\n");
+	if (x86_hyper_type == X86_HYPER_MS_HYPERV)
+		pvspin = false;
 	return 0;
 }
 early_param("hv_nopvspin", hv_parse_nopvspin);
-- 
1.8.3.1

Re: [PATCH v2 0/3] Add a unified parameter "nopvspin"

[Zhenzhong Duan]

On 2019/9/30 20:08, Zhenzhong Duan wrote:
> There are cases folks want to disable spinlock optimization for
> debug/test purpose. Xen and hyperv already have parameters "xen_nopvspin"
> and "hv_nopvspin" to support that, but kvm doesn't.
>
> The first patch adds that feature to KVM guest with "nopvspin".
>
> For compatibility reason original parameters "xen_nopvspin" and
> "hv_nopvspin" are retained and marked obsolete.
>
> v2:
> PATCH1: pick the print code change into seperate PATCH2,
>          updated patch description             [Vitaly Kuznetsov]
> PATCH2: new patch with print code change      [Vitaly Kuznetsov]

Sorry, please ignore this mail thread, just found the indentation in 
PATCH2 is wrong. I'll send a v3 later.

Thanks

Zhenzhong