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

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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>
This commit is contained in:
Sean Christopherson 2025-06-11 14:35:49 -07:00
parent 77a74b8ff4
commit 61423c413a
5 changed files with 8 additions and 56 deletions
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1
arch/x86/include/asm/kvm_host.h
View File

@ -1397,7 +1397,6 @@ struct kvm_arch {
bool pause_in_guest;
bool cstate_in_guest;
unsigned long irq_sources_bitmap;
s64 kvmclock_offset;
/*

55
arch/x86/kvm/i8254.c
View File

@ -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 @@ struct kvm_pit *kvm_create_pit(struct kvm *kvm, u32 flags)
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);
}
}

1
arch/x86/kvm/i8254.h
View File

@ -44,7 +44,6 @@ struct kvm_pit {
struct kvm_io_device speaker_dev;
struct kvm *kvm;
struct kvm_kpit_state pit_state;
int irq_source_id;
struct kvm_irq_mask_notifier mask_notifier;
struct kthread_worker *worker;
struct kthread_work expired;

6
arch/x86/kvm/x86.c
View File

@ -12669,12 +12669,6 @@ int kvm_arch_init_vm(struct kvm *kvm, unsigned long type)
INIT_HLIST_HEAD(&kvm->arch.mask_notifier_list);
atomic_set(&kvm->arch.noncoherent_dma_count, 0);
/* Reserve bit 0 of irq_sources_bitmap for userspace irq source */
set_bit(KVM_USERSPACE_IRQ_SOURCE_ID, &kvm->arch.irq_sources_bitmap);
/* Reserve bit 1 of irq_sources_bitmap for irqfd-resampler */
set_bit(KVM_IRQFD_RESAMPLE_IRQ_SOURCE_ID,
&kvm->arch.irq_sources_bitmap);
raw_spin_lock_init(&kvm->arch.tsc_write_lock);
mutex_init(&kvm->arch.apic_map_lock);
seqcount_raw_spinlock_init(&kvm->arch.pvclock_sc, &kvm->arch.tsc_write_lock);

1
include/linux/kvm_host.h
View File

@ -190,6 +190,7 @@ bool kvm_make_all_cpus_request(struct kvm *kvm, unsigned int req);
#define KVM_USERSPACE_IRQ_SOURCE_ID 0
#define KVM_IRQFD_RESAMPLE_IRQ_SOURCE_ID 1
#define KVM_PIT_IRQ_SOURCE_ID 2
extern struct mutex kvm_lock;
extern struct list_head vm_list;