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From: Zachary Amsden on 12 Jul 2010 22:10
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 <zamsden(a)redhat.com>
---
arch/x86/include/asm/kvm_host.h | 4 +++-
arch/x86/kvm/svm.c | 31 ++++++++++++++++++-------------
arch/x86/kvm/vmx.c | 22 ++++++++--------------
arch/x86/kvm/x86.c | 17 ++++++++++++++++-
arch/x86/kvm/x86.h | 2 ++
5 files changed, 47 insertions(+), 29 deletions(-)

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 502e53f..3b4efe2 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -394,8 +394,8 @@ struct kvm_arch {
gpa_t ept_identity_map_addr;

unsigned long irq_sources_bitmap;
- u64 vm_init_tsc;
s64 kvmclock_offset;
+ spinlock_t tsc_write_lock;

struct kvm_xen_hvm_config xen_hvm_config;

@@ -522,6 +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 56c9b6b..6671053 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -2543,20 +2543,9 @@ 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: {
- u64 tsc_offset = data - native_read_tsc();
- u64 g_tsc_offset = 0;
-
- if (is_nested(svm)) {
- g_tsc_offset = svm->vmcb->control.tsc_offset -
- svm->nested.hsave->control.tsc_offset;
- svm->nested.hsave->control.tsc_offset = tsc_offset;
- }
-
- svm->vmcb->control.tsc_offset = tsc_offset + g_tsc_offset;
-
+ case MSR_IA32_TSC:
+ guest_write_tsc(vcpu, data);
break;
- }
case MSR_K6_STAR:
svm->vmcb->save.star = data;
break;
@@ -3429,6 +3418,20 @@ static bool svm_has_wbinvd_exit(void)
return true;
}

+static void svm_write_tsc_offset(struct kvm_vcpu *vcpu, u64 offset)
+{
+ struct vcpu_svm *svm = to_svm(vcpu);
+ u64 g_tsc_offset = 0;
+
+ if (is_nested(svm)) {
+ g_tsc_offset = svm->vmcb->control.tsc_offset -
+ svm->nested.hsave->control.tsc_offset;
+ svm->nested.hsave->control.tsc_offset = offset;
+ }
+
+ svm->vmcb->control.tsc_offset = offset + g_tsc_offset;
+}
+
static void svm_fpu_deactivate(struct kvm_vcpu *vcpu)
{
struct vcpu_svm *svm = to_svm(vcpu);
@@ -3515,6 +3518,8 @@ 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 2fdcc98..9055ca6 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -1153,12 +1153,11 @@ 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 guest_write_tsc(u64 guest_tsc, u64 host_tsc)
+static void vmx_write_tsc_offset(struct kvm_vcpu *vcpu, u64 offset)
{
- vmcs_write64(TSC_OFFSET, guest_tsc - host_tsc);
+ vmcs_write64(TSC_OFFSET, offset);
}

/*
@@ -1231,7 +1230,6 @@ 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) {
@@ -1261,8 +1259,7 @@ 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);
- guest_write_tsc(data, host_tsc);
+ guest_write_tsc(vcpu, data);
break;
case MSR_IA32_CR_PAT:
if (vmcs_config.vmentry_ctrl & VM_ENTRY_LOAD_IA32_PAT) {
@@ -2517,7 +2514,7 @@ static int vmx_vcpu_setup(struct vcpu_vmx *vmx)
{
u32 host_sysenter_cs, msr_low, msr_high;
u32 junk;
- u64 host_pat, tsc_this, tsc_base;
+ u64 host_pat;
unsigned long a;
struct desc_ptr dt;
int i;
@@ -2658,12 +2655,7 @@ 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);

- tsc_base = vmx->vcpu.kvm->arch.vm_init_tsc;
- rdtscll(tsc_this);
- if (tsc_this < vmx->vcpu.kvm->arch.vm_init_tsc)
- tsc_base = tsc_this;
-
- guest_write_tsc(0, tsc_base);
+ guest_write_tsc(&vmx->vcpu, 0);

return 0;
}
@@ -4358,6 +4350,8 @@ 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 6ed3176..a2ee975 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -893,6 +893,21 @@ 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 guest_write_tsc(struct kvm_vcpu *vcpu, u64 data)
+{
+ struct kvm *kvm = vcpu->kvm;
+ u64 offset;
+
+ spin_lock(&kvm->arch.tsc_write_lock);
+ offset = data - native_read_tsc();
+ kvm_x86_ops->write_tsc_offset(vcpu, offset);
+ spin_unlock(&kvm->arch.tsc_write_lock);
+
+ /* Reset of TSC must disable overshoot protection below */
+ vcpu->arch.hv_clock.tsc_timestamp = 0;
+}
+EXPORT_SYMBOL_GPL(guest_write_tsc);
+
static void kvm_write_guest_time(struct kvm_vcpu *v)
{
struct timespec ts;
@@ -5487,7 +5502,7 @@ 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);

- rdtscll(kvm->arch.vm_init_tsc);
+ 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..f8d81f4 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 guest_write_tsc(struct kvm_vcpu *vcpu, u64 data);
+
#endif
--
1.7.1

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Prev: [PATCH 10/18] Keep SMP VMs more in sync on unstable TSC
Next: [PATCH 05/18] Make cpu_tsc_khz updates use local CPU