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    Subject[PATCH 16/42] KVM: Drop kvm->irq_lock lock from irq injection path
    Date
    From: Gleb Natapov <gleb@redhat.com>

    The only thing it protects now is interrupt injection into lapic and
    this can work lockless. Even now with kvm->irq_lock in place access
    to lapic is not entirely serialized since vcpu access doesn't take
    kvm->irq_lock.

    Signed-off-by: Gleb Natapov <gleb@redhat.com>
    Signed-off-by: Avi Kivity <avi@redhat.com>
    ---
    arch/ia64/kvm/kvm-ia64.c | 2 --
    arch/x86/kvm/i8254.c | 2 --
    arch/x86/kvm/lapic.c | 2 --
    arch/x86/kvm/x86.c | 2 --
    virt/kvm/eventfd.c | 2 --
    virt/kvm/irq_comm.c | 6 +-----
    virt/kvm/kvm_main.c | 2 --
    7 files changed, 1 insertions(+), 17 deletions(-)

    diff --git a/arch/ia64/kvm/kvm-ia64.c b/arch/ia64/kvm/kvm-ia64.c
    index 4a98314..f534e0f 100644
    --- a/arch/ia64/kvm/kvm-ia64.c
    +++ b/arch/ia64/kvm/kvm-ia64.c
    @@ -982,10 +982,8 @@ long kvm_arch_vm_ioctl(struct file *filp,
    goto out;
    if (irqchip_in_kernel(kvm)) {
    __s32 status;
    - mutex_lock(&kvm->irq_lock);
    status = kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID,
    irq_event.irq, irq_event.level);
    - mutex_unlock(&kvm->irq_lock);
    if (ioctl == KVM_IRQ_LINE_STATUS) {
    irq_event.status = status;
    if (copy_to_user(argp, &irq_event,
    diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
    index 144e7f6..fab7440 100644
    --- a/arch/x86/kvm/i8254.c
    +++ b/arch/x86/kvm/i8254.c
    @@ -688,10 +688,8 @@ static void __inject_pit_timer_intr(struct kvm *kvm)
    struct kvm_vcpu *vcpu;
    int i;

    - mutex_lock(&kvm->irq_lock);
    kvm_set_irq(kvm, kvm->arch.vpit->irq_source_id, 0, 1);
    kvm_set_irq(kvm, kvm->arch.vpit->irq_source_id, 0, 0);
    - mutex_unlock(&kvm->irq_lock);

    /*
    * Provides NMI watchdog support via Virtual Wire mode.
    diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
    index df8bcb0..8787637 100644
    --- a/arch/x86/kvm/lapic.c
    +++ b/arch/x86/kvm/lapic.c
    @@ -501,9 +501,7 @@ static void apic_send_ipi(struct kvm_lapic *apic)
    irq.trig_mode, irq.level, irq.dest_mode, irq.delivery_mode,
    irq.vector);

    - mutex_lock(&apic->vcpu->kvm->irq_lock);
    kvm_irq_delivery_to_apic(apic->vcpu->kvm, apic, &irq);
    - mutex_unlock(&apic->vcpu->kvm->irq_lock);
    }

    static u32 apic_get_tmcct(struct kvm_lapic *apic)
    diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
    index fdf989f..5beb4c1 100644
    --- a/arch/x86/kvm/x86.c
    +++ b/arch/x86/kvm/x86.c
    @@ -2286,10 +2286,8 @@ long kvm_arch_vm_ioctl(struct file *filp,
    goto out;
    if (irqchip_in_kernel(kvm)) {
    __s32 status;
    - mutex_lock(&kvm->irq_lock);
    status = kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID,
    irq_event.irq, irq_event.level);
    - mutex_unlock(&kvm->irq_lock);
    if (ioctl == KVM_IRQ_LINE_STATUS) {
    irq_event.status = status;
    if (copy_to_user(argp, &irq_event,
    diff --git a/virt/kvm/eventfd.c b/virt/kvm/eventfd.c
    index bb4ebd8..30f70fd 100644
    --- a/virt/kvm/eventfd.c
    +++ b/virt/kvm/eventfd.c
    @@ -61,10 +61,8 @@ irqfd_inject(struct work_struct *work)
    struct _irqfd *irqfd = container_of(work, struct _irqfd, inject);
    struct kvm *kvm = irqfd->kvm;

    - mutex_lock(&kvm->irq_lock);
    kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID, irqfd->gsi, 1);
    kvm_set_irq(kvm, KVM_USERSPACE_IRQ_SOURCE_ID, irqfd->gsi, 0);
    - mutex_unlock(&kvm->irq_lock);
    }

    /*
    diff --git a/virt/kvm/irq_comm.c b/virt/kvm/irq_comm.c
    index fadf440..15a83b9 100644
    --- a/virt/kvm/irq_comm.c
    +++ b/virt/kvm/irq_comm.c
    @@ -82,8 +82,6 @@ int kvm_irq_delivery_to_apic(struct kvm *kvm, struct kvm_lapic *src,
    int i, r = -1;
    struct kvm_vcpu *vcpu, *lowest = NULL;

    - WARN_ON(!mutex_is_locked(&kvm->irq_lock));
    -
    if (irq->dest_mode == 0 && irq->dest_id == 0xff &&
    kvm_is_dm_lowest_prio(irq))
    printk(KERN_INFO "kvm: apic: phys broadcast and lowest prio\n");
    @@ -138,7 +136,7 @@ static int kvm_set_msi(struct kvm_kernel_irq_routing_entry *e,
    return kvm_irq_delivery_to_apic(kvm, NULL, &irq);
    }

    -/* This should be called with the kvm->irq_lock mutex held
    +/*
    * Return value:
    * < 0 Interrupt was ignored (masked or not delivered for other reasons)
    * = 0 Interrupt was coalesced (previous irq is still pending)
    @@ -153,8 +151,6 @@ int kvm_set_irq(struct kvm *kvm, int irq_source_id, u32 irq, int level)

    trace_kvm_set_irq(irq, level, irq_source_id);

    - WARN_ON(!mutex_is_locked(&kvm->irq_lock));
    -
    /* Not possible to detect if the guest uses the PIC or the
    * IOAPIC. So set the bit in both. The guest will ignore
    * writes to the unused one.
    diff --git a/virt/kvm/kvm_main.c b/virt/kvm/kvm_main.c
    index 6eca153..c12c95b 100644
    --- a/virt/kvm/kvm_main.c
    +++ b/virt/kvm/kvm_main.c
    @@ -137,7 +137,6 @@ static void kvm_assigned_dev_interrupt_work_handler(struct work_struct *work)
    interrupt_work);
    kvm = assigned_dev->kvm;

    - mutex_lock(&kvm->irq_lock);
    spin_lock_irq(&assigned_dev->assigned_dev_lock);
    if (assigned_dev->irq_requested_type & KVM_DEV_IRQ_HOST_MSIX) {
    struct kvm_guest_msix_entry *guest_entries =
    @@ -156,7 +155,6 @@ static void kvm_assigned_dev_interrupt_work_handler(struct work_struct *work)
    assigned_dev->guest_irq, 1);

    spin_unlock_irq(&assigned_dev->assigned_dev_lock);
    - mutex_unlock(&assigned_dev->kvm->irq_lock);
    }

    static irqreturn_t kvm_assigned_dev_intr(int irq, void *dev_id)
    --
    1.6.5.2


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