From: Sean Christopherson sean.j.christopherson@intel.com
commit 39497d7660d9866a47a2dc9055672358da57ad3d upstream.
Automatically adjusting the globally-shared timer advancement could corrupt the timer, e.g. if multiple vCPUs are concurrently adjusting the advancement value. That could be partially fixed by using a local variable for the arithmetic, but it would still be susceptible to a race when setting timer_advance_adjust_done.
And because virtual_tsc_khz and tsc_scaling_ratio are per-vCPU, the correct calibration for a given vCPU may not apply to all vCPUs.
Furthermore, lapic_timer_advance_ns is marked __read_mostly, which is effectively violated when finding a stable advancement takes an extended amount of timer.
Opportunistically change the definition of lapic_timer_advance_ns to a u32 so that it matches the style of struct kvm_timer. Explicitly pass the param to kvm_create_lapic() so that it doesn't have to be exposed to lapic.c, thus reducing the probability of unintentionally using the global value instead of the per-vCPU value.
Cc: Liran Alon liran.alon@oracle.com Cc: Wanpeng Li wanpengli@tencent.com Reviewed-by: Liran Alon liran.alon@oracle.com Cc: stable@vger.kernel.org Fixes: 3b8a5df6c4dc6 ("KVM: LAPIC: Tune lapic_timer_advance_ns automatically") Signed-off-by: Sean Christopherson sean.j.christopherson@intel.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/kvm/lapic.c | 36 +++++++++++++++++++----------------- arch/x86/kvm/lapic.h | 4 +++- arch/x86/kvm/vmx/vmx.c | 4 +++- arch/x86/kvm/x86.c | 7 +++---- arch/x86/kvm/x86.h | 2 -- 5 files changed, 28 insertions(+), 25 deletions(-)
--- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -70,7 +70,6 @@ #define APIC_BROADCAST 0xFF #define X2APIC_BROADCAST 0xFFFFFFFFul
-static bool lapic_timer_advance_adjust_done = false; #define LAPIC_TIMER_ADVANCE_ADJUST_DONE 100 /* step-by-step approximation to mitigate fluctuation */ #define LAPIC_TIMER_ADVANCE_ADJUST_STEP 8 @@ -1482,6 +1481,7 @@ static bool lapic_timer_int_injected(str void wait_lapic_expire(struct kvm_vcpu *vcpu) { struct kvm_lapic *apic = vcpu->arch.apic; + u32 timer_advance_ns = apic->lapic_timer.timer_advance_ns; u64 guest_tsc, tsc_deadline, ns;
if (!lapic_in_kernel(vcpu)) @@ -1501,34 +1501,36 @@ void wait_lapic_expire(struct kvm_vcpu * /* __delay is delay_tsc whenever the hardware has TSC, thus always. */ if (guest_tsc < tsc_deadline) __delay(min(tsc_deadline - guest_tsc, - nsec_to_cycles(vcpu, lapic_timer_advance_ns))); + nsec_to_cycles(vcpu, timer_advance_ns)));
- if (!lapic_timer_advance_adjust_done) { + if (!apic->lapic_timer.timer_advance_adjust_done) { /* too early */ if (guest_tsc < tsc_deadline) { ns = (tsc_deadline - guest_tsc) * 1000000ULL; do_div(ns, vcpu->arch.virtual_tsc_khz); - lapic_timer_advance_ns -= min((unsigned int)ns, - lapic_timer_advance_ns / LAPIC_TIMER_ADVANCE_ADJUST_STEP); + timer_advance_ns -= min((u32)ns, + timer_advance_ns / LAPIC_TIMER_ADVANCE_ADJUST_STEP); } else { /* too late */ ns = (guest_tsc - tsc_deadline) * 1000000ULL; do_div(ns, vcpu->arch.virtual_tsc_khz); - lapic_timer_advance_ns += min((unsigned int)ns, - lapic_timer_advance_ns / LAPIC_TIMER_ADVANCE_ADJUST_STEP); + timer_advance_ns += min((u32)ns, + timer_advance_ns / LAPIC_TIMER_ADVANCE_ADJUST_STEP); } if (abs(guest_tsc - tsc_deadline) < LAPIC_TIMER_ADVANCE_ADJUST_DONE) - lapic_timer_advance_adjust_done = true; - if (unlikely(lapic_timer_advance_ns > 5000)) { - lapic_timer_advance_ns = 0; - lapic_timer_advance_adjust_done = true; + apic->lapic_timer.timer_advance_adjust_done = true; + if (unlikely(timer_advance_ns > 5000)) { + timer_advance_ns = 0; + apic->lapic_timer.timer_advance_adjust_done = true; } + apic->lapic_timer.timer_advance_ns = timer_advance_ns; } }
static void start_sw_tscdeadline(struct kvm_lapic *apic) { - u64 guest_tsc, tscdeadline = apic->lapic_timer.tscdeadline; + struct kvm_timer *ktimer = &apic->lapic_timer; + u64 guest_tsc, tscdeadline = ktimer->tscdeadline; u64 ns = 0; ktime_t expire; struct kvm_vcpu *vcpu = apic->vcpu; @@ -1548,11 +1550,10 @@ static void start_sw_tscdeadline(struct do_div(ns, this_tsc_khz);
if (likely(tscdeadline > guest_tsc) && - likely(ns > lapic_timer_advance_ns)) { + likely(ns > apic->lapic_timer.timer_advance_ns)) { expire = ktime_add_ns(now, ns); - expire = ktime_sub_ns(expire, lapic_timer_advance_ns); - hrtimer_start(&apic->lapic_timer.timer, - expire, HRTIMER_MODE_ABS_PINNED); + expire = ktime_sub_ns(expire, ktimer->timer_advance_ns); + hrtimer_start(&ktimer->timer, expire, HRTIMER_MODE_ABS_PINNED); } else apic_timer_expired(apic);
@@ -2259,7 +2260,7 @@ static enum hrtimer_restart apic_timer_f return HRTIMER_NORESTART; }
-int kvm_create_lapic(struct kvm_vcpu *vcpu) +int kvm_create_lapic(struct kvm_vcpu *vcpu, u32 timer_advance_ns) { struct kvm_lapic *apic;
@@ -2283,6 +2284,7 @@ int kvm_create_lapic(struct kvm_vcpu *vc hrtimer_init(&apic->lapic_timer.timer, CLOCK_MONOTONIC, HRTIMER_MODE_ABS_PINNED); apic->lapic_timer.timer.function = apic_timer_fn; + apic->lapic_timer.timer_advance_ns = timer_advance_ns;
/* * APIC is created enabled. This will prevent kvm_lapic_set_base from --- a/arch/x86/kvm/lapic.h +++ b/arch/x86/kvm/lapic.h @@ -31,8 +31,10 @@ struct kvm_timer { u32 timer_mode_mask; u64 tscdeadline; u64 expired_tscdeadline; + u32 timer_advance_ns; atomic_t pending; /* accumulated triggered timers */ bool hv_timer_in_use; + bool timer_advance_adjust_done; };
struct kvm_lapic { @@ -62,7 +64,7 @@ struct kvm_lapic {
struct dest_map;
-int kvm_create_lapic(struct kvm_vcpu *vcpu); +int kvm_create_lapic(struct kvm_vcpu *vcpu, u32 timer_advance_ns); void kvm_free_lapic(struct kvm_vcpu *vcpu);
int kvm_apic_has_interrupt(struct kvm_vcpu *vcpu); --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -7133,6 +7133,7 @@ static int vmx_set_hv_timer(struct kvm_v { struct vcpu_vmx *vmx; u64 tscl, guest_tscl, delta_tsc, lapic_timer_advance_cycles; + struct kvm_timer *ktimer = &vcpu->arch.apic->lapic_timer;
if (kvm_mwait_in_guest(vcpu->kvm)) return -EOPNOTSUPP; @@ -7141,7 +7142,8 @@ static int vmx_set_hv_timer(struct kvm_v tscl = rdtsc(); guest_tscl = kvm_read_l1_tsc(vcpu, tscl); delta_tsc = max(guest_deadline_tsc, guest_tscl) - guest_tscl; - lapic_timer_advance_cycles = nsec_to_cycles(vcpu, lapic_timer_advance_ns); + lapic_timer_advance_cycles = nsec_to_cycles(vcpu, + ktimer->timer_advance_ns);
if (delta_tsc > lapic_timer_advance_cycles) delta_tsc -= lapic_timer_advance_cycles; --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -137,9 +137,8 @@ static u32 __read_mostly tsc_tolerance_p module_param(tsc_tolerance_ppm, uint, S_IRUGO | S_IWUSR);
/* lapic timer advance (tscdeadline mode only) in nanoseconds */ -unsigned int __read_mostly lapic_timer_advance_ns = 1000; +static u32 __read_mostly lapic_timer_advance_ns = 1000; module_param(lapic_timer_advance_ns, uint, S_IRUGO | S_IWUSR); -EXPORT_SYMBOL_GPL(lapic_timer_advance_ns);
static bool __read_mostly vector_hashing = true; module_param(vector_hashing, bool, S_IRUGO); @@ -7882,7 +7881,7 @@ static int vcpu_enter_guest(struct kvm_v }
trace_kvm_entry(vcpu->vcpu_id); - if (lapic_timer_advance_ns) + if (vcpu->arch.apic->lapic_timer.timer_advance_ns) wait_lapic_expire(vcpu); guest_enter_irqoff();
@@ -9070,7 +9069,7 @@ int kvm_arch_vcpu_init(struct kvm_vcpu * goto fail_free_pio_data;
if (irqchip_in_kernel(vcpu->kvm)) { - r = kvm_create_lapic(vcpu); + r = kvm_create_lapic(vcpu, lapic_timer_advance_ns); if (r < 0) goto fail_mmu_destroy; } else --- a/arch/x86/kvm/x86.h +++ b/arch/x86/kvm/x86.h @@ -294,8 +294,6 @@ extern u64 kvm_supported_xcr0(void);
extern unsigned int min_timer_period_us;
-extern unsigned int lapic_timer_advance_ns; - extern bool enable_vmware_backdoor;
extern struct static_key kvm_no_apic_vcpu;