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Code Issues Releases Wiki Activity

KVM: x86: Move "KVM no-APIC vCPU" key management into local APIC code

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Move incrementing and decrementing of kvm_has_noapic_vcpu into
kvm_create_lapic() and kvm_free_lapic() respectively to fix a benign bug
where KVM fails to decrement the count if vCPU creation ultimately fails,
e.g. due to a memory allocation failing.

Note, the bug is benign as kvm_has_noapic_vcpu is used purely to optimize
lapic_in_kernel() checks, and that optimization is quite dubious.  That,
and practically speaking no setup that cares at all about performance runs
with a userspace local APIC.

Reported-by: Li RongQing <lirongqing@baidu.com>
Cc: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Xu Yilun <yilun.xu@linux.intel.com>
Link: https://lore.kernel.org/r/20240209222047.394389-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>
This commit is contained in:
Sean Christopherson 2024-02-09 14:20:46 -08:00
parent 0ec3d6d1f1
commit a78d904669
2 changed files with 29 additions and 27 deletions
Show stats Download patch file Download diff file Expand all files Collapse all files

27
arch/x86/kvm/lapic.c
View file

@ -124,6 +124,9 @@ static inline int __apic_test_and_clear_vector(int vec, void *bitmap)
return __test_and_clear_bit(VEC_POS(vec), (bitmap) + REG_POS(vec));
}
__read_mostly DEFINE_STATIC_KEY_FALSE(kvm_has_noapic_vcpu);
EXPORT_SYMBOL_GPL(kvm_has_noapic_vcpu);
__read_mostly DEFINE_STATIC_KEY_DEFERRED_FALSE(apic_hw_disabled, HZ);
__read_mostly DEFINE_STATIC_KEY_DEFERRED_FALSE(apic_sw_disabled, HZ);
@ -2466,8 +2469,10 @@ void kvm_free_lapic(struct kvm_vcpu *vcpu)
{
struct kvm_lapic *apic = vcpu->arch.apic;
if (!vcpu->arch.apic)
if (!vcpu->arch.apic) {
static_branch_dec(&kvm_has_noapic_vcpu);
return;
}
hrtimer_cancel(&apic->lapic_timer.timer);
@ -2809,6 +2814,11 @@ int kvm_create_lapic(struct kvm_vcpu *vcpu, int timer_advance_ns)
ASSERT(vcpu != NULL);
if (!irqchip_in_kernel(vcpu->kvm)) {
static_branch_inc(&kvm_has_noapic_vcpu);
return 0;
}
apic = kzalloc(sizeof(*apic), GFP_KERNEL_ACCOUNT);
if (!apic)
goto nomem;
@ -2844,6 +2854,21 @@ int kvm_create_lapic(struct kvm_vcpu *vcpu, int timer_advance_ns)
static_branch_inc(&apic_sw_disabled.key); /* sw disabled at reset */
kvm_iodevice_init(&apic->dev, &apic_mmio_ops);
/*
* Defer evaluating inhibits until the vCPU is first run, as this vCPU
* will not get notified of any changes until this vCPU is visible to
* other vCPUs (marked online and added to the set of vCPUs).
*
* Opportunistically mark APICv active as VMX in particularly is highly
* unlikely to have inhibits. Ignore the current per-VM APICv state so
* that vCPU creation is guaranteed to run with a deterministic value,
* the request will ensure the vCPU gets the correct state before VM-Entry.
*/
if (enable_apicv) {
apic->apicv_active = true;
kvm_make_request(KVM_REQ_APICV_UPDATE, vcpu);
}
return 0;
nomem_free_apic:
kfree(apic);

29
arch/x86/kvm/x86.c
View file

@ -12046,27 +12046,9 @@ int kvm_arch_vcpu_create(struct kvm_vcpu *vcpu)
if (r < 0)
return r;
if (irqchip_in_kernel(vcpu->kvm)) {
r = kvm_create_lapic(vcpu, lapic_timer_advance_ns);
if (r < 0)
goto fail_mmu_destroy;
/*
* Defer evaluating inhibits until the vCPU is first run, as
* this vCPU will not get notified of any changes until this
* vCPU is visible to other vCPUs (marked online and added to
* the set of vCPUs). Opportunistically mark APICv active as
* VMX in particularly is highly unlikely to have inhibits.
* Ignore the current per-VM APICv state so that vCPU creation
* is guaranteed to run with a deterministic value, the request
* will ensure the vCPU gets the correct state before VM-Entry.
*/
if (enable_apicv) {
vcpu->arch.apic->apicv_active = true;
kvm_make_request(KVM_REQ_APICV_UPDATE, vcpu);
}
} else
static_branch_inc(&kvm_has_noapic_vcpu);
r = kvm_create_lapic(vcpu, lapic_timer_advance_ns);
if (r < 0)
goto fail_mmu_destroy;
r = -ENOMEM;
@ -12187,8 +12169,6 @@ void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)
srcu_read_unlock(&vcpu->kvm->srcu, idx);
free_page((unsigned long)vcpu->arch.pio_data);
kvfree(vcpu->arch.cpuid_entries);
if (!lapic_in_kernel(vcpu))
static_branch_dec(&kvm_has_noapic_vcpu);
}
void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
@ -12465,9 +12445,6 @@ bool kvm_vcpu_is_bsp(struct kvm_vcpu *vcpu)
return (vcpu->arch.apic_base & MSR_IA32_APICBASE_BSP) != 0;
}
__read_mostly DEFINE_STATIC_KEY_FALSE(kvm_has_noapic_vcpu);
EXPORT_SYMBOL_GPL(kvm_has_noapic_vcpu);
void kvm_arch_sched_in(struct kvm_vcpu *vcpu, int cpu)
{
struct kvm_pmu *pmu = vcpu_to_pmu(vcpu);