Re: [PATCH v9 17/18] KVM: Update Posted-Interrupts Descriptor when vCPU is blocked

From: Paolo Bonzini
Date: Fri Sep 18 2015 - 12:07:07 EST



On 18/09/2015 16:29, Feng Wu wrote:
> This patch updates the Posted-Interrupts Descriptor when vCPU
> is blocked.
>
> pre-block:
> - Add the vCPU to the blocked per-CPU list
> - Set 'NV' to POSTED_INTR_WAKEUP_VECTOR
>
> post-block:
> - Remove the vCPU from the per-CPU list
>
> Signed-off-by: Feng Wu <feng.wu-ral2JQCrhuEAvxtiuMwx3w@xxxxxxxxxxxxxxxx>
> ---
> v9:
> - Add description for blocked_vcpu_on_cpu_lock in Documentation/virtual/kvm/locking.txt
> - Check !kvm_arch_has_assigned_device(vcpu->kvm) first, then
> !irq_remapping_cap(IRQ_POSTING_CAP)
>
> v8:
> - Rename 'pi_pre_block' to 'pre_block'
> - Rename 'pi_post_block' to 'post_block'
> - Change some comments
> - Only add the vCPU to the blocking list when the VM has assigned devices.
>
> Documentation/virtual/kvm/locking.txt | 12 +++
> arch/x86/include/asm/kvm_host.h | 13 +++
> arch/x86/kvm/vmx.c | 153 ++++++++++++++++++++++++++++++++++
> arch/x86/kvm/x86.c | 53 +++++++++---
> include/linux/kvm_host.h | 3 +
> virt/kvm/kvm_main.c | 3 +
> 6 files changed, 227 insertions(+), 10 deletions(-)
>
> diff --git a/Documentation/virtual/kvm/locking.txt b/Documentation/virtual/kvm/locking.txt
> index d68af4d..19f94a6 100644
> --- a/Documentation/virtual/kvm/locking.txt
> +++ b/Documentation/virtual/kvm/locking.txt
> @@ -166,3 +166,15 @@ Comment: The srcu read lock must be held while accessing memslots (e.g.
> MMIO/PIO address->device structure mapping (kvm->buses).
> The srcu index can be stored in kvm_vcpu->srcu_idx per vcpu
> if it is needed by multiple functions.
> +
> +Name: blocked_vcpu_on_cpu_lock
> +Type: spinlock_t
> +Arch: x86
> +Protects: blocked_vcpu_on_cpu
> +Comment: This is a per-CPU lock and it is used for VT-d posted-interrupts.
> + When VT-d posted-interrupts is supported and the VM has assigned
> + devices, we put the blocked vCPU on the list blocked_vcpu_on_cpu
> + protected by blocked_vcpu_on_cpu_lock, when VT-d hardware issues
> + wakeup notification event since external interrupts from the
> + assigned devices happens, we will find the vCPU on the list to
> + wakeup.
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 0ddd353..304fbb5 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -552,6 +552,8 @@ struct kvm_vcpu_arch {
> */
> bool write_fault_to_shadow_pgtable;
>
> + bool halted;
> +
> /* set at EPT violation at this point */
> unsigned long exit_qualification;
>
> @@ -864,6 +866,17 @@ struct kvm_x86_ops {
> /* pmu operations of sub-arch */
> const struct kvm_pmu_ops *pmu_ops;
>
> + /*
> + * Architecture specific hooks for vCPU blocking due to
> + * HLT instruction.
> + * Returns for .pre_block():
> + * - 0 means continue to block the vCPU.
> + * - 1 means we cannot block the vCPU since some event
> + * happens during this period, such as, 'ON' bit in
> + * posted-interrupts descriptor is set.
> + */
> + int (*pre_block)(struct kvm_vcpu *vcpu);
> + void (*post_block)(struct kvm_vcpu *vcpu);
> int (*update_pi_irte)(struct kvm *kvm, unsigned int host_irq,
> uint32_t guest_irq, bool set);
> };
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 902a67d..9968896 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -879,6 +879,13 @@ static DEFINE_PER_CPU(struct vmcs *, current_vmcs);
> static DEFINE_PER_CPU(struct list_head, loaded_vmcss_on_cpu);
> static DEFINE_PER_CPU(struct desc_ptr, host_gdt);
>
> +/*
> + * We maintian a per-CPU linked-list of vCPU, so in wakeup_handler() we
> + * can find which vCPU should be waken up.
> + */
> +static DEFINE_PER_CPU(struct list_head, blocked_vcpu_on_cpu);
> +static DEFINE_PER_CPU(spinlock_t, blocked_vcpu_on_cpu_lock);
> +
> static unsigned long *vmx_io_bitmap_a;
> static unsigned long *vmx_io_bitmap_b;
> static unsigned long *vmx_msr_bitmap_legacy;
> @@ -2985,6 +2992,8 @@ static int hardware_enable(void)
> return -EBUSY;
>
> INIT_LIST_HEAD(&per_cpu(loaded_vmcss_on_cpu, cpu));
> + INIT_LIST_HEAD(&per_cpu(blocked_vcpu_on_cpu, cpu));
> + spin_lock_init(&per_cpu(blocked_vcpu_on_cpu_lock, cpu));
>
> /*
> * Now we can enable the vmclear operation in kdump
> @@ -6121,6 +6130,25 @@ static void update_ple_window_actual_max(void)
> ple_window_grow, INT_MIN);
> }
>
> +/*
> + * Handler for POSTED_INTERRUPT_WAKEUP_VECTOR.
> + */
> +static void wakeup_handler(void)
> +{
> + struct kvm_vcpu *vcpu;
> + int cpu = smp_processor_id();
> +
> + spin_lock(&per_cpu(blocked_vcpu_on_cpu_lock, cpu));
> + list_for_each_entry(vcpu, &per_cpu(blocked_vcpu_on_cpu, cpu),
> + blocked_vcpu_list) {
> + struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu);
> +
> + if (pi_test_on(pi_desc) == 1)
> + kvm_vcpu_kick(vcpu);
> + }
> + spin_unlock(&per_cpu(blocked_vcpu_on_cpu_lock, cpu));
> +}
> +
> static __init int hardware_setup(void)
> {
> int r = -ENOMEM, i, msr;
> @@ -6305,6 +6333,8 @@ static __init int hardware_setup(void)
> kvm_x86_ops->enable_log_dirty_pt_masked = NULL;
> }
>
> + kvm_set_posted_intr_wakeup_handler(wakeup_handler);
> +
> return alloc_kvm_area();
>
> out8:
> @@ -10430,6 +10460,126 @@ static void vmx_enable_log_dirty_pt_masked(struct kvm *kvm,
> }
>
> /*
> + * 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:
> + * 'NDST' <-- vcpu->pre_pcpu
> + * '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.
> + *
> + */
> +static int vmx_pre_block(struct kvm_vcpu *vcpu)
> +{
> + unsigned long flags;
> + unsigned int dest;
> + struct pi_desc old, new;
> + struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu);
> +
> + if (!kvm_arch_has_assigned_device(vcpu->kvm) ||
> + !irq_remapping_cap(IRQ_POSTING_CAP))
> + return 0;
> +
> + vcpu->pre_pcpu = vcpu->cpu;
> + spin_lock_irqsave(&per_cpu(blocked_vcpu_on_cpu_lock,
> + vcpu->pre_pcpu), flags);
> + list_add_tail(&vcpu->blocked_vcpu_list,
> + &per_cpu(blocked_vcpu_on_cpu,
> + vcpu->pre_pcpu));
> + spin_unlock_irqrestore(&per_cpu(blocked_vcpu_on_cpu_lock,
> + vcpu->pre_pcpu), flags);
> +
> + do {
> + old.control = new.control = pi_desc->control;
> +
> + /*
> + * We should not block the vCPU if
> + * an interrupt is posted for it.
> + */
> + if (pi_test_on(pi_desc) == 1) {
> + spin_lock_irqsave(&per_cpu(blocked_vcpu_on_cpu_lock,
> + vcpu->pre_pcpu), flags);
> + list_del(&vcpu->blocked_vcpu_list);
> + spin_unlock_irqrestore(
> + &per_cpu(blocked_vcpu_on_cpu_lock,
> + vcpu->pre_pcpu), flags);
> + vcpu->pre_pcpu = -1;
> +
> + return 1;
> + }
> +
> + WARN((pi_desc->sn == 1),
> + "Warning: SN field of posted-interrupts "
> + "is set before blocking\n");
> +
> + /*
> + * Since vCPU can be preempted during this process,
> + * vcpu->cpu could be different with pre_pcpu, we
> + * need to set pre_pcpu as the destination of wakeup
> + * notification event, then we can find the right vCPU
> + * to wakeup in wakeup handler if interrupts happen
> + * when the vCPU is in blocked state.
> + */
> + dest = cpu_physical_id(vcpu->pre_pcpu);
> +
> + if (x2apic_enabled())
> + new.ndst = dest;
> + else
> + new.ndst = (dest << 8) & 0xFF00;
> +
> + /* set 'NV' to 'wakeup vector' */
> + new.nv = POSTED_INTR_WAKEUP_VECTOR;
> + } while (cmpxchg(&pi_desc->control, old.control,
> + new.control) != old.control);
> +
> + return 0;
> +}
> +
> +static void vmx_post_block(struct kvm_vcpu *vcpu)
> +{
> + struct pi_desc *pi_desc = vcpu_to_pi_desc(vcpu);
> + struct pi_desc old, new;
> + unsigned int dest;
> + unsigned long flags;
> +
> + if (!kvm_arch_has_assigned_device(vcpu->kvm) ||
> + !irq_remapping_cap(IRQ_POSTING_CAP))
> + return;
> +
> + do {
> + old.control = new.control = pi_desc->control;
> +
> + dest = cpu_physical_id(vcpu->cpu);
> +
> + if (x2apic_enabled())
> + new.ndst = dest;
> + else
> + new.ndst = (dest << 8) & 0xFF00;
> +
> + /* Allow posting non-urgent interrupts */
> + new.sn = 0;
> +
> + /* set 'NV' to 'notification vector' */
> + new.nv = POSTED_INTR_VECTOR;
> + } while (cmpxchg(&pi_desc->control, old.control,
> + new.control) != old.control);
> +
> + if(vcpu->pre_pcpu != -1) {
> + spin_lock_irqsave(
> + &per_cpu(blocked_vcpu_on_cpu_lock,
> + vcpu->pre_pcpu), flags);
> + list_del(&vcpu->blocked_vcpu_list);
> + spin_unlock_irqrestore(
> + &per_cpu(blocked_vcpu_on_cpu_lock,
> + vcpu->pre_pcpu), flags);
> + vcpu->pre_pcpu = -1;
> + }
> +}
> +
> +/*
> * vmx_update_pi_irte - set IRTE for Posted-Interrupts
> *
> * @kvm: kvm
> @@ -10620,6 +10770,9 @@ static struct kvm_x86_ops vmx_x86_ops = {
> .flush_log_dirty = vmx_flush_log_dirty,
> .enable_log_dirty_pt_masked = vmx_enable_log_dirty_pt_masked,
>
> + .pre_block = vmx_pre_block,
> + .post_block = vmx_post_block,
> +
> .pmu_ops = &intel_pmu_ops,
>
> .update_pi_irte = vmx_update_pi_irte,
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index 58688aa..46f55b2 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -5869,7 +5869,12 @@ int kvm_vcpu_halt(struct kvm_vcpu *vcpu)
> {
> ++vcpu->stat.halt_exits;
> if (irqchip_in_kernel(vcpu->kvm)) {
> - vcpu->arch.mp_state = KVM_MP_STATE_HALTED;
> + /* Handle posted-interrupt when vCPU is to be halted */
> + if (!kvm_x86_ops->pre_block ||
> + kvm_x86_ops->pre_block(vcpu) == 0) {
> + vcpu->arch.halted = true;
> + vcpu->arch.mp_state = KVM_MP_STATE_HALTED;
> + }
> return 1;
> } else {
> vcpu->run->exit_reason = KVM_EXIT_HLT;
> @@ -6518,6 +6523,20 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
> kvm_vcpu_reload_apic_access_page(vcpu);
> }
>
> + /*
> + * KVM_REQ_EVENT is not set when posted interrupts are set by
> + * VT-d hardware, so we have to update RVI unconditionally.
> + */
> + if (kvm_lapic_enabled(vcpu)) {
> + /*
> + * Update architecture specific hints for APIC
> + * virtual interrupt delivery.
> + */
> + if (kvm_x86_ops->hwapic_irr_update)
> + kvm_x86_ops->hwapic_irr_update(vcpu,
> + kvm_lapic_find_highest_irr(vcpu));
> + }
> +
> if (kvm_check_request(KVM_REQ_EVENT, vcpu) || req_int_win) {
> kvm_apic_accept_events(vcpu);
> if (vcpu->arch.mp_state == KVM_MP_STATE_INIT_RECEIVED) {
> @@ -6534,13 +6553,6 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu)
> kvm_x86_ops->enable_irq_window(vcpu);
>
> if (kvm_lapic_enabled(vcpu)) {
> - /*
> - * Update architecture specific hints for APIC
> - * virtual interrupt delivery.
> - */
> - if (kvm_x86_ops->hwapic_irr_update)
> - kvm_x86_ops->hwapic_irr_update(vcpu,
> - kvm_lapic_find_highest_irr(vcpu));
> update_cr8_intercept(vcpu);
> kvm_lapic_sync_to_vapic(vcpu);
> }
> @@ -6711,10 +6723,31 @@ static int vcpu_run(struct kvm_vcpu *vcpu)
>
> for (;;) {
> if (vcpu->arch.mp_state == KVM_MP_STATE_RUNNABLE &&
> - !vcpu->arch.apf.halted)
> + !vcpu->arch.apf.halted) {
> + /*
> + * For some cases, we can get here with
> + * vcpu->arch.halted being true.
> + */


Feng,

can you explain what are the reasons for this?

Perhaps pre_block and post_block should be handled entirely in
vcpu_block, like this:

static inline int vcpu_block(struct kvm *kvm, struct kvm_vcpu *vcpu)
{
- if (!kvm_arch_vcpu_runnable(vcpu)) {
+ if (!kvm_arch_vcpu_runnable(vcpu) &&
+ (!kvm_x86_ops->pre_block || kvm_x86_ops->pre_block(vcpu) == 0)) {
srcu_read_unlock(&kvm->srcu, vcpu->srcu_idx);
kvm_vcpu_block(vcpu);
vcpu->srcu_idx = srcu_read_lock(&kvm->srcu);
+
+ if (kvm_x86_ops->post_block)
+ kvm_x86_ops->post_block(vcpu);
+
if (!kvm_check_request(KVM_REQ_UNHALT, vcpu))
return 1;
}

and removing all of your changes in kvm_vcpu_halt and vcpu_run?
(Full patch below my signature, only compile-tested).

It should not matter if mp_state goes briefly to KVM_MP_STATE_HALTED and
from there back to KVM_MP_STATE_RUNNABLE.

Paolo

diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index 4a0b1a800317..5265a5522458 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -568,8 +568,6 @@ struct kvm_vcpu_arch {
*/
bool write_fault_to_shadow_pgtable;

- bool halted;
-
/* set at EPT violation at this point */
unsigned long exit_qualification;

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index a2a070541318..44092cfa1c0a 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -5674,12 +5674,7 @@ int kvm_vcpu_halt(struct kvm_vcpu *vcpu)
{
++vcpu->stat.halt_exits;
if (irqchip_in_kernel(vcpu->kvm)) {
- /* Handle posted-interrupt when vCPU is to be halted */
- if (!kvm_x86_ops->pre_block ||
- kvm_x86_ops->pre_block(vcpu) == 0) {
- vcpu->arch.halted = true;
- vcpu->arch.mp_state = KVM_MP_STATE_HALTED;
- }
+ vcpu->arch.mp_state = KVM_MP_STATE_HALTED;
return 1;
} else {
vcpu->run->exit_reason = KVM_EXIT_HLT;
@@ -6446,10 +6441,15 @@ out:

static inline int vcpu_block(struct kvm *kvm, struct kvm_vcpu *vcpu)
{
- if (!kvm_arch_vcpu_runnable(vcpu)) {
+ if (!kvm_arch_vcpu_runnable(vcpu) &&
+ (!kvm_x86_ops->pre_block || kvm_x86_ops->pre_block(vcpu) == 0)) {
srcu_read_unlock(&kvm->srcu, vcpu->srcu_idx);
kvm_vcpu_block(vcpu);
vcpu->srcu_idx = srcu_read_lock(&kvm->srcu);
+
+ if (kvm_x86_ops->post_block)
+ kvm_x86_ops->post_block(vcpu);
+
if (!kvm_check_request(KVM_REQ_UNHALT, vcpu))
return 1;
}
@@ -6482,28 +6482,9 @@ static int vcpu_run(struct kvm_vcpu *vcpu)
for (;;) {
if (vcpu->arch.mp_state == KVM_MP_STATE_RUNNABLE &&
!vcpu->arch.apf.halted) {
- /*
- * For some cases, we can get here with
- * vcpu->arch.halted being true.
- */
- if (kvm_x86_ops->post_block && vcpu->arch.halted) {
- kvm_x86_ops->post_block(vcpu);
- vcpu->arch.halted = false;
- }
-
r = vcpu_enter_guest(vcpu);
} else {
r = vcpu_block(kvm, vcpu);
-
- /*
- * post_block() must be called after
- * pre_block() which is called in
- * kvm_vcpu_halt().
- */
- if (kvm_x86_ops->post_block && vcpu->arch.halted) {
- kvm_x86_ops->post_block(vcpu);
- vcpu->arch.halted = false;
- }
}

if (r <= 0)
--
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