[PATCH 5.0 022/122] KVM: lapic: Track lapic timer advance per vCPU

Greg Kroah-Hartman
2019-05-06T14:35:21Z

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;