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KVM: x86: Refactor tsc synchronization code

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Refactor kvm_synchronize_tsc to make a new function that allows callers
to specify TSC parameters (offset, value, nanoseconds, etc.) explicitly
for the sake of participating in TSC synchronization.

Signed-off-by: Oliver Upton <oupton@google.com>
Message-Id: <20210916181538.968978-7-oupton@google.com>
[Make sure kvm->arch.cur_tsc_generation and vcpu->arch.this_tsc_generation are
 equal at the end of __kvm_synchronize_tsc, if matched is false. Reported by
 Maxim Levitsky. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Oliver Upton 2021-09-16 18:15:37 +00:00 committed by Paolo Bonzini
parent 869b44211a
commit 58d4277be9
1 changed files with 53 additions and 42 deletions
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95
arch/x86/kvm/x86.c
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@ -2435,13 +2435,63 @@ static inline bool kvm_check_tsc_unstable(void)
return check_tsc_unstable();
}
/*
* Infers attempts to synchronize the guest's tsc from host writes. Sets the
* offset for the vcpu and tracks the TSC matching generation that the vcpu
* participates in.
*/
static void __kvm_synchronize_tsc(struct kvm_vcpu *vcpu, u64 offset, u64 tsc,
u64 ns, bool matched)
{
struct kvm *kvm = vcpu->kvm;
lockdep_assert_held(&kvm->arch.tsc_write_lock);
/*
* We also track th most recent recorded KHZ, write and time to
* allow the matching interval to be extended at each write.
*/
kvm->arch.last_tsc_nsec = ns;
kvm->arch.last_tsc_write = tsc;
kvm->arch.last_tsc_khz = vcpu->arch.virtual_tsc_khz;
vcpu->arch.last_guest_tsc = tsc;
kvm_vcpu_write_tsc_offset(vcpu, offset);
if (!matched) {
/*
* We split periods of matched TSC writes into generations.
* For each generation, we track the original measured
* nanosecond time, offset, and write, so if TSCs are in
* sync, we can match exact offset, and if not, we can match
* exact software computation in compute_guest_tsc()
*
* These values are tracked in kvm->arch.cur_xxx variables.
*/
kvm->arch.cur_tsc_generation++;
kvm->arch.cur_tsc_nsec = ns;
kvm->arch.cur_tsc_write = tsc;
kvm->arch.cur_tsc_offset = offset;
kvm->arch.nr_vcpus_matched_tsc = 0;
} else if (vcpu->arch.this_tsc_generation != kvm->arch.cur_tsc_generation) {
kvm->arch.nr_vcpus_matched_tsc++;
}
/* Keep track of which generation this VCPU has synchronized to */
vcpu->arch.this_tsc_generation = kvm->arch.cur_tsc_generation;
vcpu->arch.this_tsc_nsec = kvm->arch.cur_tsc_nsec;
vcpu->arch.this_tsc_write = kvm->arch.cur_tsc_write;
kvm_track_tsc_matching(vcpu);
}
static void kvm_synchronize_tsc(struct kvm_vcpu *vcpu, u64 data)
{
struct kvm *kvm = vcpu->kvm;
u64 offset, ns, elapsed;
unsigned long flags;
bool matched;
bool already_matched;
bool matched = false;
bool synchronizing = false;
raw_spin_lock_irqsave(&kvm->arch.tsc_write_lock, flags);
@ -2487,48 +2537,9 @@ static void kvm_synchronize_tsc(struct kvm_vcpu *vcpu, u64 data)
offset = kvm_compute_l1_tsc_offset(vcpu, data);
}
matched = true;
already_matched = (vcpu->arch.this_tsc_generation == kvm->arch.cur_tsc_generation);
} else {
/*
* We split periods of matched TSC writes into generations.
* For each generation, we track the original measured
* nanosecond time, offset, and write, so if TSCs are in
* sync, we can match exact offset, and if not, we can match
* exact software computation in compute_guest_tsc()
*
* These values are tracked in kvm->arch.cur_xxx variables.
*/
kvm->arch.cur_tsc_generation++;
kvm->arch.cur_tsc_nsec = ns;
kvm->arch.cur_tsc_write = data;
kvm->arch.cur_tsc_offset = offset;
matched = false;
}
/*
* We also track th most recent recorded KHZ, write and time to
* allow the matching interval to be extended at each write.
*/
kvm->arch.last_tsc_nsec = ns;
kvm->arch.last_tsc_write = data;
kvm->arch.last_tsc_khz = vcpu->arch.virtual_tsc_khz;
vcpu->arch.last_guest_tsc = data;
/* Keep track of which generation this VCPU has synchronized to */
vcpu->arch.this_tsc_generation = kvm->arch.cur_tsc_generation;
vcpu->arch.this_tsc_nsec = kvm->arch.cur_tsc_nsec;
vcpu->arch.this_tsc_write = kvm->arch.cur_tsc_write;
kvm_vcpu_write_tsc_offset(vcpu, offset);
if (!matched) {
kvm->arch.nr_vcpus_matched_tsc = 0;
} else if (!already_matched) {
kvm->arch.nr_vcpus_matched_tsc++;
}
kvm_track_tsc_matching(vcpu);
__kvm_synchronize_tsc(vcpu, offset, data, ns, matched);
raw_spin_unlock_irqrestore(&kvm->arch.tsc_write_lock, flags);
}