[PATCH v4 5/5] x86, kvm: support vcpu preempted check

Pan Xinhui
2016-10-19T10:20:16Z

This is to fix some lock holder preemption issues. Some other locks
implementation do a spin loop before acquiring the lock itself.
Currently kernel has an interface of bool vcpu_is_preempted(int cpu). It
takes the cpu as parameter and return true if the cpu is preempted. Then
kernel can break the spin loops upon on the retval of vcpu_is_preempted.

As kernel has used this interface, So lets support it.

We use one field of struct kvm_steal_time to indicate that if one vcpu
is running or not.

unix benchmark result:
host: kernel 4.8.1, i5-4570, 4 cpus
guest: kernel 4.8.1, 8 vcpus

test-case after-patch before-patch
Execl Throughput | 18307.9 lps | 11701.6 lps
File Copy 1024 bufsize 2000 maxblocks | 1352407.3 KBps | 790418.9 KBps
File Copy 256 bufsize 500 maxblocks | 367555.6 KBps | 222867.7 KBps
File Copy 4096 bufsize 8000 maxblocks | 3675649.7 KBps | 1780614.4 KBps
Pipe Throughput | 11872208.7 lps | 11855628.9 lps
Pipe-based Context Switching | 1495126.5 lps | 1490533.9 lps
Process Creation | 29881.2 lps | 28572.8 lps
Shell Scripts (1 concurrent) | 23224.3 lpm | 22607.4 lpm
Shell Scripts (8 concurrent) | 3531.4 lpm | 3211.9 lpm
System Call Overhead | 10385653.0 lps | 10419979.0 lps

Signed-off-by: Pan Xinhui <xinhui.pan@linux.vnet.ibm.com>
---
arch/x86/include/asm/paravirt_types.h | 6 ++++++
arch/x86/include/asm/spinlock.h | 8 ++++++++
arch/x86/include/uapi/asm/kvm_para.h | 3 ++-
arch/x86/kernel/kvm.c | 11 +++++++++++
arch/x86/kernel/paravirt.c | 11 +++++++++++
arch/x86/kvm/x86.c | 12 ++++++++++++
6 files changed, 50 insertions(+), 1 deletion(-)

diff --git a/arch/x86/include/asm/paravirt_types.h b/arch/x86/include/asm/paravirt_types.h
index 0f400c0..b1c7937 100644
--- a/arch/x86/include/asm/paravirt_types.h
+++ b/arch/x86/include/asm/paravirt_types.h
@@ -98,6 +98,10 @@ struct pv_time_ops {
unsigned long long (*steal_clock)(int cpu);
};

+struct pv_vcpu_ops {
+ bool (*vcpu_is_preempted)(int cpu);
+};
+
struct pv_cpu_ops {
/* hooks for various privileged instructions */
unsigned long (*get_debugreg)(int regno);
@@ -318,6 +322,7 @@ struct pv_lock_ops {
struct paravirt_patch_template {
struct pv_init_ops pv_init_ops;
struct pv_time_ops pv_time_ops;
+ struct pv_vcpu_ops pv_vcpu_ops;
struct pv_cpu_ops pv_cpu_ops;
struct pv_irq_ops pv_irq_ops;
struct pv_mmu_ops pv_mmu_ops;
@@ -327,6 +332,7 @@ struct paravirt_patch_template {
extern struct pv_info pv_info;
extern struct pv_init_ops pv_init_ops;
extern struct pv_time_ops pv_time_ops;
+extern struct pv_vcpu_ops pv_vcpu_ops;
extern struct pv_cpu_ops pv_cpu_ops;
extern struct pv_irq_ops pv_irq_ops;
extern struct pv_mmu_ops pv_mmu_ops;
diff --git a/arch/x86/include/asm/spinlock.h b/arch/x86/include/asm/spinlock.h
index 921bea7..52fd942 100644
--- a/arch/x86/include/asm/spinlock.h
+++ b/arch/x86/include/asm/spinlock.h
@@ -26,6 +26,14 @@
extern struct static_key paravirt_ticketlocks_enabled;
static __always_inline bool static_key_false(struct static_key *key);

+#ifdef CONFIG_PARAVIRT
+#define vcpu_is_preempted vcpu_is_preempted
+static inline bool vcpu_is_preempted(int cpu)
+{
+ return pv_vcpu_ops.vcpu_is_preempted(cpu);
+}
+#endif
+
#include <asm/qspinlock.h>

/*
diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h
index 94dc8ca..e9c12a1 100644
--- a/arch/x86/include/uapi/asm/kvm_para.h
+++ b/arch/x86/include/uapi/asm/kvm_para.h
@@ -45,7 +45,8 @@ struct kvm_steal_time {
__u64 steal;
__u32 version;
__u32 flags;
- __u32 pad[12];
+ __u32 preempted;
+ __u32 pad[11];
};

#define KVM_STEAL_ALIGNMENT_BITS 5
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index edbbfc8..0011bef 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -415,6 +415,15 @@ void kvm_disable_steal_time(void)
wrmsr(MSR_KVM_STEAL_TIME, 0, 0);
}

+static bool kvm_vcpu_is_preempted(int cpu)
+{
+ struct kvm_steal_time *src;
+
+ src = &per_cpu(steal_time, cpu);
+
+ return !!src->preempted;
+}
+
#ifdef CONFIG_SMP
static void __init kvm_smp_prepare_boot_cpu(void)
{
@@ -488,6 +497,8 @@ void __init kvm_guest_init(void)
kvm_guest_cpu_init();
#endif

+ pv_vcpu_ops.vcpu_is_preempted = kvm_vcpu_is_preempted;
+
/*
* Hard lockup detection is enabled by default. Disable it, as guests
* can get false positives too easily, for example if the host is
diff --git a/arch/x86/kernel/paravirt.c b/arch/x86/kernel/paravirt.c
index bbf3d59..7adb7e9 100644
--- a/arch/x86/kernel/paravirt.c
+++ b/arch/x86/kernel/paravirt.c
@@ -122,6 +122,7 @@ static void *get_call_destination(u8 type)
struct paravirt_patch_template tmpl = {
.pv_init_ops = pv_init_ops,
.pv_time_ops = pv_time_ops,
+ .pv_vcpu_ops = pv_vcpu_ops,
.pv_cpu_ops = pv_cpu_ops,
.pv_irq_ops = pv_irq_ops,
.pv_mmu_ops = pv_mmu_ops,
@@ -203,6 +204,11 @@ static u64 native_steal_clock(int cpu)
return 0;
}

+static bool native_vcpu_is_preempted(int cpu)
+{
+ return 0;
+}
+
/* These are in entry.S */
extern void native_iret(void);
extern void native_usergs_sysret64(void);
@@ -312,6 +318,10 @@ struct pv_time_ops pv_time_ops = {
.steal_clock = native_steal_clock,
};

+struct pv_vcpu_ops pv_vcpu_ops = {
+ .vcpu_is_preempted = native_vcpu_is_preempted,
+};
+
__visible struct pv_irq_ops pv_irq_ops = {
.save_fl = __PV_IS_CALLEE_SAVE(native_save_fl),
.restore_fl = __PV_IS_CALLEE_SAVE(native_restore_fl),
@@ -458,6 +468,7 @@ struct pv_mmu_ops pv_mmu_ops __ro_after_init = {
};

EXPORT_SYMBOL_GPL(pv_time_ops);
+EXPORT_SYMBOL (pv_vcpu_ops);
EXPORT_SYMBOL (pv_cpu_ops);
EXPORT_SYMBOL (pv_mmu_ops);
EXPORT_SYMBOL_GPL(pv_info);
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 6c633de..0ffc5aa 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2057,6 +2057,8 @@ static void record_steal_time(struct kvm_vcpu *vcpu)
&vcpu->arch.st.steal, sizeof(struct kvm_steal_time))))
return;

+ vcpu->arch.st.steal.preempted = 0;
+
if (vcpu->arch.st.steal.version & 1)
vcpu->arch.st.steal.version += 1; /* first time write, random junk */

@@ -2812,6 +2814,16 @@ void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu)

void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
{
+ if (vcpu->arch.st.msr_val & KVM_MSR_ENABLED)
+ if (kvm_read_guest_cached(vcpu->kvm, &vcpu->arch.st.stime,
+ &vcpu->arch.st.steal,
+ sizeof(struct kvm_steal_time)) == 0) {
+ vcpu->arch.st.steal.preempted = 1;
+ kvm_write_guest_cached(vcpu->kvm, &vcpu->arch.st.stime,
+ &vcpu->arch.st.steal,
+ sizeof(struct kvm_steal_time));
+ }
+
kvm_x86_ops->vcpu_put(vcpu);
kvm_put_guest_fpu(vcpu);
vcpu->arch.last_host_tsc = rdtsc();
--
2.4.11