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Message-ID: <20250519232808.2745331-8-seanjc@google.com>
Date: Mon, 19 May 2025 16:28:00 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Sean Christopherson <seanjc@...gle.com>, Paolo Bonzini <pbonzini@...hat.com>,
Vitaly Kuznetsov <vkuznets@...hat.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: [PATCH 07/15] 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.
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
arch/x86/include/asm/kvm_host.h | 1 -
arch/x86/kvm/i8254.c | 55 +++++----------------------------
arch/x86/kvm/i8254.h | 1 -
arch/x86/kvm/x86.c | 6 ----
include/linux/kvm_host.h | 1 +
5 files changed, 8 insertions(+), 56 deletions(-)
diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
index f25ec3ec5ce4..c8654e461933 100644
--- a/arch/x86/include/asm/kvm_host.h
+++ b/arch/x86/include/asm/kvm_host.h
@@ -1396,7 +1396,6 @@ struct kvm_arch {
bool pause_in_guest;
bool cstate_in_guest;
- unsigned long irq_sources_bitmap;
s64 kvmclock_offset;
/*
diff --git a/arch/x86/kvm/i8254.c b/arch/x86/kvm/i8254.c
index 2a0964c859af..d4fc20c265b2 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_kernel(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);
}
@@ -715,10 +679,6 @@ 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));
@@ -770,8 +730,7 @@ 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;
}
@@ -788,7 +747,7 @@ 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);
}
}
diff --git a/arch/x86/kvm/i8254.h b/arch/x86/kvm/i8254.h
index a768212ba821..14fb310357f2 100644
--- a/arch/x86/kvm/i8254.h
+++ b/arch/x86/kvm/i8254.h
@@ -42,7 +42,6 @@ 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;
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 4a9c252c9dab..9e2c249d45ca 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -12790,12 +12790,6 @@ 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);
diff --git a/include/linux/kvm_host.h b/include/linux/kvm_host.h
index 0d4506598d62..44b439c5fcf4 100644
--- a/include/linux/kvm_host.h
+++ b/include/linux/kvm_host.h
@@ -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;
--
2.49.0.1101.gccaa498523-goog
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