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Subject[PATCH 2/4] KVM: x86: rewrite handling of scaled TSC for kvmclock
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This is the same as before:

kvm_scale_tsc(tgt_tsc_khz)
= tgt_tsc_khz * ratio
= tgt_tsc_khz * user_tsc_khz / tsc_khz (see set_tsc_khz)
= user_tsc_khz (see kvm_guest_time_update)
= vcpu->arch.virtual_tsc_khz (see kvm_set_tsc_khz)

However, computing it through kvm_scale_tsc makes it possible
to include the NTP correction in tgt_tsc_khz, as done in the
next patch.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
arch/x86/kvm/x86.c | 15 ++++++++-------
1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 1ca2b44f70bb..6db3c219795b 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1713,7 +1713,7 @@ static void kvm_gen_update_masterclock(struct kvm *kvm)

static int kvm_guest_time_update(struct kvm_vcpu *v)
{
- unsigned long flags, this_tsc_khz, tgt_tsc_khz;
+ unsigned long flags, tgt_tsc_khz;
struct kvm_vcpu_arch *vcpu = &v->arch;
struct kvm_arch *ka = &v->kvm->arch;
s64 kernel_ns;
@@ -1739,8 +1739,8 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)

/* Keep irq disabled to prevent changes to the clock */
local_irq_save(flags);
- this_tsc_khz = __this_cpu_read(cpu_tsc_khz);
- if (unlikely(this_tsc_khz == 0)) {
+ tgt_tsc_khz = __this_cpu_read(cpu_tsc_khz);
+ if (unlikely(tgt_tsc_khz == 0)) {
local_irq_restore(flags);
kvm_make_request(KVM_REQ_CLOCK_UPDATE, v);
return 1;
@@ -1775,13 +1775,14 @@ static int kvm_guest_time_update(struct kvm_vcpu *v)
if (!vcpu->pv_time_enabled)
return 0;

- if (unlikely(vcpu->hw_tsc_khz != this_tsc_khz)) {
- tgt_tsc_khz = kvm_has_tsc_control ?
- vcpu->virtual_tsc_khz : this_tsc_khz;
+ if (kvm_has_tsc_control)
+ tgt_tsc_khz = kvm_scale_tsc(v, tgt_tsc_khz);
+
+ if (unlikely(vcpu->hw_tsc_khz != tgt_tsc_khz)) {
kvm_get_time_scale(NSEC_PER_SEC / 1000, tgt_tsc_khz,
&vcpu->hv_clock.tsc_shift,
&vcpu->hv_clock.tsc_to_system_mul);
- vcpu->hw_tsc_khz = this_tsc_khz;
+ vcpu->hw_tsc_khz = tgt_tsc_khz;
}

/* With all the info we got, fill in the values */
--
1.8.3.1

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