KVM: x86: Hardcode the PIT IRQ source ID to '2'

Hardcode the PIT's source IRQ ID to '2' instead of "finding" that bit 2
is always the first available bit in irq_sources_bitmap.  Bits 0 and 1 are
set/reserved by kvm_arch_init_vm(), i.e. long before kvm_create_pit() can
be invoked, and KVM allows at most one in-kernel PIT instance, i.e. it's
impossible for the PIT to find a different free bit (there are no other
users of kvm_request_irq_source_id().

Delete the now-defunct irq_sources_bitmap and all its associated code.

Acked-by: Kai Huang <kai.huang@intel.com>
Link: https://lore.kernel.org/r/20250611213557.294358-11-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

1 files changed, 7 insertions, 48 deletions

diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index 2bb223bf0dac..fa8187608cfc 100644
--- a/arch/x86/kvm/i8254.c
+++ b/arch/x86/kvm/i8254.c
@@ -248,8 +248,8 @@ static void pit_do_work(struct kthread_work *work)
 	if (atomic_read(&ps->reinject) && !atomic_xchg(&ps->irq_ack, 0))
 		return;
 
-	kvm_set_irq(kvm, pit->irq_source_id, 0, 1, false);
-	kvm_set_irq(kvm, pit->irq_source_id, 0, 0, false);
+	kvm_set_irq(kvm, KVM_PIT_IRQ_SOURCE_ID, 0, 1, false);
+	kvm_set_irq(kvm, KVM_PIT_IRQ_SOURCE_ID, 0, 0, false);
 
 	/*
 	 * Provides NMI watchdog support via Virtual Wire mode.
@@ -641,47 +641,11 @@ static void kvm_pit_reset(struct kvm_pit *pit)
 	kvm_pit_reset_reinject(pit);
 }
 
-static int kvm_request_irq_source_id(struct kvm *kvm)
+static void kvm_pit_clear_all(struct kvm *kvm)
 {
-	unsigned long *bitmap = &kvm->arch.irq_sources_bitmap;
-	int irq_source_id;
-
-	mutex_lock(&kvm->irq_lock);
-	irq_source_id = find_first_zero_bit(bitmap, BITS_PER_LONG);
-
-	if (irq_source_id >= BITS_PER_LONG) {
-		pr_warn("exhausted allocatable IRQ sources!\n");
-		irq_source_id = -EFAULT;
-		goto unlock;
-	}
-
-	ASSERT(irq_source_id != KVM_USERSPACE_IRQ_SOURCE_ID);
-	ASSERT(irq_source_id != KVM_IRQFD_RESAMPLE_IRQ_SOURCE_ID);
-	set_bit(irq_source_id, bitmap);
-unlock:
-	mutex_unlock(&kvm->irq_lock);
-
-	return irq_source_id;
-}
-
-static void kvm_free_irq_source_id(struct kvm *kvm, int irq_source_id)
-{
-	ASSERT(irq_source_id != KVM_USERSPACE_IRQ_SOURCE_ID);
-	ASSERT(irq_source_id != KVM_IRQFD_RESAMPLE_IRQ_SOURCE_ID);
-
 	mutex_lock(&kvm->irq_lock);
-	if (irq_source_id < 0 ||
-	    irq_source_id >= BITS_PER_LONG) {
-		pr_err("IRQ source ID out of range!\n");
-		goto unlock;
-	}
-	clear_bit(irq_source_id, &kvm->arch.irq_sources_bitmap);
-	if (!irqchip_full(kvm))
-		goto unlock;
-
-	kvm_ioapic_clear_all(kvm->arch.vioapic, irq_source_id);
-	kvm_pic_clear_all(kvm->arch.vpic, irq_source_id);
-unlock:
+	kvm_ioapic_clear_all(kvm->arch.vioapic, KVM_PIT_IRQ_SOURCE_ID);
+	kvm_pic_clear_all(kvm->arch.vpic, KVM_PIT_IRQ_SOURCE_ID);
 	mutex_unlock(&kvm->irq_lock);
 }
 
@@ -788,10 +752,6 @@ struct kvm_pit *kvm_create_pit(struct kvm *kvm, u32 flags)
 	if (!pit)
 		return NULL;
 
-	pit->irq_source_id = kvm_request_irq_source_id(kvm);
-	if (pit->irq_source_id < 0)
-		goto fail_request;
-
 	mutex_init(&pit->pit_state.lock);
 
 	pid = get_pid(task_tgid(current));
@@ -843,8 +803,7 @@ fail_register_pit:
 	kvm_pit_set_reinject(pit, false);
 	kthread_destroy_worker(pit->worker);
 fail_kthread:
-	kvm_free_irq_source_id(kvm, pit->irq_source_id);
-fail_request:
+	kvm_pit_clear_all(kvm);
 	kfree(pit);
 	return NULL;
 }
@@ -861,7 +820,7 @@ void kvm_free_pit(struct kvm *kvm)
 		kvm_pit_set_reinject(pit, false);
 		hrtimer_cancel(&pit->pit_state.timer);
 		kthread_destroy_worker(pit->worker);
-		kvm_free_irq_source_id(kvm, pit->irq_source_id);
+		kvm_pit_clear_all(kvm);
 		kfree(pit);
 	}
 }