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SubjectRe: [PATCH v3 1/4] x86/kvm: add boot parameter for adding vcpu-id bits
On Tue, Nov 16, 2021, Juergen Gross wrote:
> diff --git a/arch/x86/kvm/ioapic.c b/arch/x86/kvm/ioapic.c
> index 816a82515dcd..64ba9b1c8b3d 100644
> --- a/arch/x86/kvm/ioapic.c
> +++ b/arch/x86/kvm/ioapic.c
> @@ -685,11 +685,21 @@ static const struct kvm_io_device_ops ioapic_mmio_ops = {
> int kvm_ioapic_init(struct kvm *kvm)
> {
> struct kvm_ioapic *ioapic;
> + size_t sz;
> int ret;
>
> - ioapic = kzalloc(sizeof(struct kvm_ioapic), GFP_KERNEL_ACCOUNT);
> + sz = sizeof(struct kvm_ioapic) +
> + sizeof(*ioapic->rtc_status.dest_map.map) *
> + BITS_TO_LONGS(KVM_MAX_VCPU_IDS) +
> + sizeof(*ioapic->rtc_status.dest_map.vectors) *
> + (KVM_MAX_VCPU_IDS);
> + ioapic = kzalloc(sz, GFP_KERNEL_ACCOUNT);
> if (!ioapic)
> return -ENOMEM;
> + ioapic->rtc_status.dest_map.map = (void *)(ioapic + 1);

Oof. Just do separate allocations. I highly doubt the performance of the
emulated RTC hinges on the spatial locality of the bitmap and array. The array
is going to end up in a second page for most configuration anyways.

> + ioapic->rtc_status.dest_map.vectors =
> + (void *)(ioapic->rtc_status.dest_map.map +
> + BITS_TO_LONGS(KVM_MAX_VCPU_IDS));
> spin_lock_init(&ioapic->lock);
> INIT_DELAYED_WORK(&ioapic->eoi_inject, kvm_ioapic_eoi_inject_work);
> kvm->arch.vioapic = ioapic;

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