Also, ensure that the storing of the offset and the reading of the TSC
are never preempted by taking a spinlock. While the lock is overkill
now, it is useful later in this patch series.
Signed-off-by: Zachary Amsden <[email protected]>
---
arch/x86/include/asm/kvm_host.h | 3 +++
arch/x86/kvm/svm.c | 6 ++++--
arch/x86/kvm/vmx.c | 13 ++++++-------
arch/x86/kvm/x86.c | 18 ++++++++++++++++++
arch/x86/kvm/x86.h | 2 ++
5 files changed, 33 insertions(+), 9 deletions(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 960f9c9..3b4efe2 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -395,6 +395,7 @@ struct kvm_arch {
unsigned long irq_sources_bitmap;
s64 kvmclock_offset;
+ spinlock_t tsc_write_lock;
struct kvm_xen_hvm_config xen_hvm_config;
@@ -521,6 +522,8 @@ struct kvm_x86_ops {
bool (*has_wbinvd_exit)(void);
+ void (*write_tsc_offset)(struct kvm_vcpu *vcpu, u64 offset);
+
const struct trace_print_flags *exit_reasons_str;
};
diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 4cb8822..8d7ae20 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -2581,8 +2581,8 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, unsigned ecx, u64 data)
struct vcpu_svm *svm = to_svm(vcpu);
switch (ecx) {
- case MSR_IA32_TSC:
- svm_write_tsc_offset(vcpu, data - native_read_tsc());
+ case MSR_IA32_TSC:
+ kvm_write_tsc(vcpu, data);
break;
case MSR_K6_STAR:
svm->vmcb->save.star = data;
@@ -3547,6 +3547,8 @@ static struct kvm_x86_ops svm_x86_ops = {
.set_supported_cpuid = svm_set_supported_cpuid,
.has_wbinvd_exit = svm_has_wbinvd_exit,
+
+ .write_tsc_offset = svm_write_tsc_offset,
};
static int __init svm_init(void)
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 1f67e94..e3e056f 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -1152,10 +1152,9 @@ static u64 guest_read_tsc(void)
}
/*
- * writes 'guest_tsc' into guest's timestamp counter "register"
- * guest_tsc = host_tsc + tsc_offset ==> tsc_offset = guest_tsc - host_tsc
+ * writes 'offset' into guest's timestamp counter offset register
*/
-static void vmx_write_tsc_offset(u64 offset)
+static void vmx_write_tsc_offset(struct kvm_vcpu *vcpu, u64 offset)
{
vmcs_write64(TSC_OFFSET, offset);
}
@@ -1230,7 +1229,6 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, u32 msr_index, u64 data)
{
struct vcpu_vmx *vmx = to_vmx(vcpu);
struct shared_msr_entry *msr;
- u64 host_tsc;
int ret = 0;
switch (msr_index) {
@@ -1260,8 +1258,7 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, u32 msr_index, u64 data)
vmcs_writel(GUEST_SYSENTER_ESP, data);
break;
case MSR_IA32_TSC:
- rdtscll(host_tsc);
- vmx_write_tsc_offset(data - host_tsc);
+ kvm_write_tsc(vcpu, data);
break;
case MSR_IA32_CR_PAT:
if (vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_IA32_PAT) {
@@ -2659,7 +2656,7 @@ static int vmx_vcpu_setup(struct vcpu_vmx *vmx)
vmx->vcpu.arch.cr4_guest_owned_bits |= X86_CR4_PGE;
vmcs_writel(CR4_GUEST_HOST_MASK, ~vmx->vcpu.arch.cr4_guest_owned_bits);
- vmx_write_tsc_offset(0-native_read_tsc());
+ kvm_write_tsc(&vmx->vcpu, 0);
return 0;
}
@@ -4354,6 +4351,8 @@ static struct kvm_x86_ops vmx_x86_ops = {
.set_supported_cpuid = vmx_set_supported_cpuid,
.has_wbinvd_exit = cpu_has_vmx_wbinvd_exit,
+
+ .write_tsc_offset = vmx_write_tsc_offset,
};
static int __init vmx_init(void)
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 1bf9227..33e8208 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -895,6 +895,22 @@ static void kvm_set_time_scale(uint32_t tsc_khz, struct pvclock_vcpu_time_info *
static DEFINE_PER_CPU(unsigned long, cpu_tsc_khz);
+void kvm_write_tsc(struct kvm_vcpu *vcpu, u64 data)
+{
+ struct kvm *kvm = vcpu->kvm;
+ u64 offset;
+ unsigned long flags;
+
+ spin_lock_irqsave(&kvm->arch.tsc_write_lock, flags);
+ offset = data - native_read_tsc();
+ kvm_x86_ops->write_tsc_offset(vcpu, offset);
+ spin_unlock_irqrestore(&kvm->arch.tsc_write_lock, flags);
+
+ /* Reset of TSC must disable overshoot protection below */
+ vcpu->arch.hv_clock.tsc_timestamp = 0;
+}
+EXPORT_SYMBOL_GPL(kvm_write_tsc);
+
static void kvm_write_guest_time(struct kvm_vcpu *v)
{
struct timespec ts;
@@ -5495,6 +5511,8 @@ struct kvm *kvm_arch_create_vm(void)
/* Reserve bit 0 of irq_sources_bitmap for userspace irq source */
set_bit(KVM_USERSPACE_IRQ_SOURCE_ID, &kvm->arch.irq_sources_bitmap);
+ spin_lock_init(&kvm->arch.tsc_write_lock);
+
return kvm;
}
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index b7a4047..2d6385e 100644
--- a/arch/x86/kvm/x86.h
+++ b/arch/x86/kvm/x86.h
@@ -68,4 +68,6 @@ static inline int is_paging(struct kvm_vcpu *vcpu)
void kvm_before_handle_nmi(struct kvm_vcpu *vcpu);
void kvm_after_handle_nmi(struct kvm_vcpu *vcpu);
+void kvm_write_tsc(struct kvm_vcpu *vcpu, u64 data);
+
#endif
--
1.7.1
On Thu, Aug 19, 2010 at 10:07:17PM -1000, Zachary Amsden wrote:
> Also, ensure that the storing of the offset and the reading of the TSC
> are never preempted by taking a spinlock. While the lock is overkill
> now, it is useful later in this patch series.
>
> + spinlock_t tsc_write_lock;
Forgive my utter ignorance, specially if it is to become
obvious in a latter patch: This is a vcpu-local operation,
uses rdtscl, so pcpu-local too, and we don't expect
multiple writers to it at the same time.
Why do we need this lock?
On 08/20/2010 07:06 AM, Glauber Costa wrote:
> On Thu, Aug 19, 2010 at 10:07:17PM -1000, Zachary Amsden wrote:
>
>> Also, ensure that the storing of the offset and the reading of the TSC
>> are never preempted by taking a spinlock. While the lock is overkill
>> now, it is useful later in this patch series.
>>
>> + spinlock_t tsc_write_lock;
>>
> Forgive my utter ignorance, specially if it is to become
> obvious in a latter patch: This is a vcpu-local operation,
> uses rdtscl, so pcpu-local too, and we don't expect
> multiple writers to it at the same time.
>
> Why do we need this lock?
>
>
Synchronizing access to the variables which we use to match TSC writes
across multiple VCPUs.