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KVM: lapic: Track lapic timer advance per vCPU

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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: 3b8a5df6c4 ("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>
This commit is contained in:
Sean Christopherson 2019-04-17 10:15:32 -07:00 committed by Paolo Bonzini
parent 57bf67e73c
commit 39497d7660
5 changed files with 28 additions and 25 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

36
arch/x86/kvm/lapic.c
View file

@ -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
@ -1485,6 +1484,7 @@ static bool lapic_timer_int_injected(struct kvm_vcpu *vcpu)
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))
@ -1504,34 +1504,36 @@ void wait_lapic_expire(struct kvm_vcpu *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;
@ -1551,11 +1553,10 @@ static void start_sw_tscdeadline(struct kvm_lapic *apic)
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);
@ -2262,7 +2263,7 @@ static enum hrtimer_restart apic_timer_fn(struct hrtimer *data)
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;
@ -2286,6 +2287,7 @@ int kvm_create_lapic(struct kvm_vcpu *vcpu)
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

4
arch/x86/kvm/lapic.h
View file

@ -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);

4
arch/x86/kvm/vmx/vmx.c
View file

@ -7032,6 +7032,7 @@ static int vmx_set_hv_timer(struct kvm_vcpu *vcpu, u64 guest_deadline_tsc)
{
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;
@ -7040,7 +7041,8 @@ static int vmx_set_hv_timer(struct kvm_vcpu *vcpu, u64 guest_deadline_tsc)
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;

7
arch/x86/kvm/x86.c
View file

@ -137,9 +137,8 @@ static u32 __read_mostly tsc_tolerance_ppm = 250;
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);
@ -7873,7 +7872,7 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
}
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();
@ -9061,7 +9060,7 @@ int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
if (irqchip_in_kernel(vcpu->kvm)) {
vcpu->arch.apicv_active = kvm_x86_ops->get_enable_apicv(vcpu);
r = kvm_create_lapic(vcpu);
r = kvm_create_lapic(vcpu, lapic_timer_advance_ns);
if (r < 0)
goto fail_mmu_destroy;
} else

2
arch/x86/kvm/x86.h
View file

@ -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;