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KVM: VMX: Handle PI descriptor updates during vcpu_put/load

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Move the posted interrupt pre/post_block logic into vcpu_put/load
respectively, using the kvm_vcpu_is_blocking() to determining whether or
not the wakeup handler needs to be set (and unset).  This avoids updating
the PI descriptor if halt-polling is successful, reduces the number of
touchpoints for updating the descriptor, and eliminates the confusing
behavior of intentionally leaving a "stale" PI.NDST when a blocking vCPU
is scheduled back in after preemption.

The downside is that KVM will do the PID update twice if the vCPU is
preempted after prepare_to_rcuwait() but before schedule(), but that's a
rare case (and non-existent on !PREEMPT kernels).

The notable wart is the need to send a self-IPI on the wakeup vector if
an outstanding notification is pending after configuring the wakeup
vector.  Ideally, KVM would just do a kvm_vcpu_wake_up() in this case,
but the scheduler doesn't support waking a task from its preemption
notifier callback, i.e. while the task is right in the middle of
being scheduled out.

Note, setting the wakeup vector before halt-polling is not necessary:
once the pending IRQ will be recorded in the PIR, kvm_vcpu_has_events()
will detect this (via kvm_cpu_get_interrupt(), kvm_apic_get_interrupt(),
apic_has_interrupt_for_ppr() and finally vmx_sync_pir_to_irr()) and
terminate the polling.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Message-Id: <20211208015236.1616697-5-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Sean Christopherson 2021-12-08 01:52:14 +00:00 committed by Paolo Bonzini
parent 4f5a884fc2
commit d76fb40637
3 changed files with 72 additions and 95 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

154
arch/x86/kvm/vmx/posted_intr.c
View File

@ -52,6 +52,7 @@ void vmx_vcpu_pi_load(struct kvm_vcpu *vcpu, int cpu)
{
struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu);
struct pi_desc old, new;
unsigned long flags;
unsigned int dest;
/*
@ -62,23 +63,34 @@ void vmx_vcpu_pi_load(struct kvm_vcpu *vcpu, int cpu)
if (!enable_apicv || !lapic_in_kernel(vcpu))
return;
/* Nothing to do if PI.SN and PI.NDST both have the desired value. */
if (!pi_test_sn(pi_desc) && vcpu->cpu == cpu)
return;
/*
* If the 'nv' field is POSTED_INTR_WAKEUP_VECTOR, do not change
* PI.NDST: pi_post_block is the one expected to change PID.NDST and the
* wakeup handler expects the vCPU to be on the blocked_vcpu_list that
* matches PI.NDST. Otherwise, a vcpu may not be able to be woken up
* correctly.
* If the vCPU wasn't on the wakeup list and wasn't migrated, then the
* full update can be skipped as neither the vector nor the destination
* needs to be changed.
*/
if (pi_desc->nv == POSTED_INTR_WAKEUP_VECTOR || vcpu->cpu == cpu) {
pi_clear_sn(pi_desc);
goto after_clear_sn;
if (pi_desc->nv != POSTED_INTR_WAKEUP_VECTOR && vcpu->cpu == cpu) {
/*
* Clear SN if it was set due to being preempted. Again, do
* this even if there is no assigned device for simplicity.
*/
if (pi_test_and_clear_sn(pi_desc))
goto after_clear_sn;
return;
}
local_irq_save(flags);
/*
* If the vCPU was waiting for wakeup, remove the vCPU from the wakeup
* list of the _previous_ pCPU, which will not be the same as the
* current pCPU if the task was migrated.
*/
if (pi_desc->nv == POSTED_INTR_WAKEUP_VECTOR) {
raw_spin_lock(&per_cpu(blocked_vcpu_on_cpu_lock, vcpu->cpu));
list_del(&vcpu->blocked_vcpu_list);
raw_spin_unlock(&per_cpu(blocked_vcpu_on_cpu_lock, vcpu->cpu));
}
/* The full case. Set the new destination and clear SN. */
dest = cpu_physical_id(cpu);
if (!x2apic_mode)
dest = (dest << 8) & 0xFF00;
@ -86,10 +98,22 @@ void vmx_vcpu_pi_load(struct kvm_vcpu *vcpu, int cpu)
do {
old.control = new.control = READ_ONCE(pi_desc->control);
/*
* Clear SN (as above) and refresh the destination APIC ID to
* handle task migration (@cpu != vcpu->cpu).
*/
new.ndst = dest;
new.sn = 0;
/*
* Restore the notification vector; in the blocking case, the
* descriptor was modified on "put" to use the wakeup vector.
*/
new.nv = POSTED_INTR_VECTOR;
} while (pi_try_set_control(pi_desc, old.control, new.control));
local_irq_restore(flags);
after_clear_sn:
/*
@ -111,83 +135,24 @@ static bool vmx_can_use_vtd_pi(struct kvm *kvm)
irq_remapping_cap(IRQ_POSTING_CAP);
}
void vmx_vcpu_pi_put(struct kvm_vcpu *vcpu)
{
struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu);
if (!vmx_can_use_vtd_pi(vcpu->kvm))
return;
/* Set SN when the vCPU is preempted */
if (vcpu->preempted)
pi_set_sn(pi_desc);
}
static void __pi_post_block(struct kvm_vcpu *vcpu)
{
struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu);
struct pi_desc old, new;
unsigned int dest;
/*
* Remove the vCPU from the wakeup list of the _previous_ pCPU, which
* will not be the same as the current pCPU if the task was migrated.
*/
raw_spin_lock(&per_cpu(blocked_vcpu_on_cpu_lock, vcpu->pre_pcpu));
list_del(&vcpu->blocked_vcpu_list);
raw_spin_unlock(&per_cpu(blocked_vcpu_on_cpu_lock, vcpu->pre_pcpu));
dest = cpu_physical_id(vcpu->cpu);
if (!x2apic_mode)
dest = (dest << 8) & 0xFF00;
WARN(pi_desc->nv != POSTED_INTR_WAKEUP_VECTOR,
"Wakeup handler not enabled while the vCPU was blocking");
do {
old.control = new.control = READ_ONCE(pi_desc->control);
new.ndst = dest;
/* set 'NV' to 'notification vector' */
new.nv = POSTED_INTR_VECTOR;
} while (pi_try_set_control(pi_desc, old.control, new.control));
vcpu->pre_pcpu = -1;
}
/*
* This routine does the following things for vCPU which is going
* to be blocked if VT-d PI is enabled.
* - Store the vCPU to the wakeup list, so when interrupts happen
* we can find the right vCPU to wake up.
* - Change the Posted-interrupt descriptor as below:
* 'NV' <-- POSTED_INTR_WAKEUP_VECTOR
* - If 'ON' is set during this process, which means at least one
* interrupt is posted for this vCPU, we cannot block it, in
* this case, return 1, otherwise, return 0.
*
* Put the vCPU on this pCPU's list of vCPUs that needs to be awakened and set
* WAKEUP as the notification vector in the PI descriptor.
*/
int pi_pre_block(struct kvm_vcpu *vcpu)
static void pi_enable_wakeup_handler(struct kvm_vcpu *vcpu)
{
struct pi_desc old, new;
struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu);
struct pi_desc old, new;
unsigned long flags;
if (!vmx_can_use_vtd_pi(vcpu->kvm) ||
vmx_interrupt_blocked(vcpu))
return 0;
local_irq_save(flags);
vcpu->pre_pcpu = vcpu->cpu;
raw_spin_lock(&per_cpu(blocked_vcpu_on_cpu_lock, vcpu->cpu));
list_add_tail(&vcpu->blocked_vcpu_list,
&per_cpu(blocked_vcpu_on_cpu, vcpu->cpu));
raw_spin_unlock(&per_cpu(blocked_vcpu_on_cpu_lock, vcpu->cpu));
WARN(pi_desc->sn == 1,
"Posted Interrupt Suppress Notification set before blocking");
WARN(pi_desc->sn, "PI descriptor SN field set before blocking");
do {
old.control = new.control = READ_ONCE(pi_desc->control);
@ -196,24 +161,37 @@ int pi_pre_block(struct kvm_vcpu *vcpu)
new.nv = POSTED_INTR_WAKEUP_VECTOR;
} while (pi_try_set_control(pi_desc, old.control, new.control));
/* We should not block the vCPU if an interrupt is posted for it. */
if (pi_test_on(pi_desc))
__pi_post_block(vcpu);
/*
* Send a wakeup IPI to this CPU if an interrupt may have been posted
* before the notification vector was updated, in which case the IRQ
* will arrive on the non-wakeup vector. An IPI is needed as calling
* try_to_wake_up() from ->sched_out() isn't allowed (IRQs are not
* enabled until it is safe to call try_to_wake_up() on the task being
* scheduled out).
*/
if (pi_test_on(&new))
apic->send_IPI_self(POSTED_INTR_WAKEUP_VECTOR);
local_irq_restore(flags);
return (vcpu->pre_pcpu == -1);
}
void pi_post_block(struct kvm_vcpu *vcpu)
void vmx_vcpu_pi_put(struct kvm_vcpu *vcpu)
{
unsigned long flags;
struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu);
if (vcpu->pre_pcpu == -1)
if (!vmx_can_use_vtd_pi(vcpu->kvm))
return;
local_irq_save(flags);
__pi_post_block(vcpu);
local_irq_restore(flags);
if (kvm_vcpu_is_blocking(vcpu) && !vmx_interrupt_blocked(vcpu))
pi_enable_wakeup_handler(vcpu);
/*
* Set SN when the vCPU is preempted. Note, the vCPU can both be seen
* as blocking and preempted, e.g. if it's preempted between setting
* its wait state and manually scheduling out.
*/
if (vcpu->preempted)
pi_set_sn(pi_desc);
}
/*
@ -254,7 +232,7 @@ bool pi_has_pending_interrupt(struct kvm_vcpu *vcpu)
* Bail out of the block loop if the VM has an assigned
* device, but the blocking vCPU didn't reconfigure the
* PI.NV to the wakeup vector, i.e. the assigned device
* came along after the initial check in pi_pre_block().
* came along after the initial check in vmx_vcpu_pi_put().
*/
void vmx_pi_start_assignment(struct kvm *kvm)
{

8
arch/x86/kvm/vmx/posted_intr.h
View File

@ -40,6 +40,12 @@ static inline bool pi_test_and_clear_on(struct pi_desc *pi_desc)
(unsigned long *)&pi_desc->control);
}
static inline bool pi_test_and_clear_sn(struct pi_desc *pi_desc)
{
return test_and_clear_bit(POSTED_INTR_SN,
(unsigned long *)&pi_desc->control);
}
static inline bool pi_test_and_set_pir(int vector, struct pi_desc *pi_desc)
{
return test_and_set_bit(vector, (unsigned long *)pi_desc->pir);
@ -88,8 +94,6 @@ static inline bool pi_test_sn(struct pi_desc *pi_desc)
void vmx_vcpu_pi_load(struct kvm_vcpu *vcpu, int cpu);
void vmx_vcpu_pi_put(struct kvm_vcpu *vcpu);
int pi_pre_block(struct kvm_vcpu *vcpu);
void pi_post_block(struct kvm_vcpu *vcpu);
void pi_wakeup_handler(void);
void __init pi_init_cpu(int cpu);
bool pi_has_pending_interrupt(struct kvm_vcpu *vcpu);

5
arch/x86/kvm/vmx/vmx.c
View File

@ -7566,9 +7566,6 @@ void vmx_update_cpu_dirty_logging(struct kvm_vcpu *vcpu)
static int vmx_pre_block(struct kvm_vcpu *vcpu)
{
if (pi_pre_block(vcpu))
return 1;
if (kvm_lapic_hv_timer_in_use(vcpu))
kvm_lapic_switch_to_sw_timer(vcpu);
@ -7579,8 +7576,6 @@ static void vmx_post_block(struct kvm_vcpu *vcpu)
{
if (kvm_x86_ops.set_hv_timer)
kvm_lapic_switch_to_hv_timer(vcpu);
pi_post_block(vcpu);
}
static void vmx_setup_mce(struct kvm_vcpu *vcpu)