Re: [PATCH v3 09/34] KVM: x86: hyper-v: Don't use sparse_set_to_vcpu_mask() in kvm_hv_send_ipi()

Maxim Levitsky
2022-05-11T11:25:56Z

On Thu, 2022-04-14 at 15:19 +0200, Vitaly Kuznetsov wrote:
> Get rid of on-stack allocation of vcpu_mask and optimize kvm_hv_send_ipi()
> for a smaller number of vCPUs in the request. When Hyper-V TLB flush
> is in use, HvSendSyntheticClusterIpi{,Ex} calls are not commonly used to
> send IPIs to a large number of vCPUs (and are rarely used in general).
>
> Introduce hv_is_vp_in_sparse_set() to directly check if the specified
> VP_ID is present in sparse vCPU set.
>
> Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
> ---
> arch/x86/kvm/hyperv.c | 37 ++++++++++++++++++++++++++-----------
> 1 file changed, 26 insertions(+), 11 deletions(-)
>
> diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
> index 3cf68645a2e6..aebbb598ad1d 100644
> --- a/arch/x86/kvm/hyperv.c
> +++ b/arch/x86/kvm/hyperv.c
> @@ -1746,6 +1746,25 @@ static void sparse_set_to_vcpu_mask(struct kvm *kvm, u64 *sparse_banks,
> }
> }
>
> +static bool hv_is_vp_in_sparse_set(u32 vp_id, u64 valid_bank_mask, u64 sparse_banks[])
> +{
> + int bank, sbank = 0;
> +
> + if (!test_bit(vp_id / HV_VCPUS_PER_SPARSE_BANK,
> + (unsigned long *)&valid_bank_mask))
> + return false;
> +
> + for_each_set_bit(bank, (unsigned long *)&valid_bank_mask,
> + KVM_HV_MAX_SPARSE_VCPU_SET_BITS) {
> + if (bank == vp_id / HV_VCPUS_PER_SPARSE_BANK)
> + break;
> + sbank++;
> + }
> +
> + return test_bit(vp_id % HV_VCPUS_PER_SPARSE_BANK,
> + (unsigned long *)&sparse_banks[sbank]);
> +}
> +
> struct kvm_hv_hcall {
> u64 param;
> u64 ingpa;
> @@ -2089,8 +2108,8 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
> ((u64)hc->rep_cnt << HV_HYPERCALL_REP_COMP_OFFSET);
> }
>
> -static void kvm_send_ipi_to_many(struct kvm *kvm, u32 vector,
> - unsigned long *vcpu_bitmap)
> +static void kvm_hv_send_ipi_to_many(struct kvm *kvm, u32 vector,
> + u64 *sparse_banks, u64 valid_bank_mask)
I think the indentation is wrong here (was wrong before as well)

> {
> struct kvm_lapic_irq irq = {
> .delivery_mode = APIC_DM_FIXED,
> @@ -2100,7 +2119,10 @@ static void kvm_send_ipi_to_many(struct kvm *kvm, u32 vector,
> unsigned long i;
>
> kvm_for_each_vcpu(i, vcpu, kvm) {
> - if (vcpu_bitmap && !test_bit(i, vcpu_bitmap))
> + if (sparse_banks &&
> + !hv_is_vp_in_sparse_set(kvm_hv_get_vpindex(vcpu),
> + valid_bank_mask,
> + sparse_banks))
> continue;
>
> /* We fail only when APIC is disabled */
> @@ -2113,7 +2135,6 @@ static u64 kvm_hv_send_ipi(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
> struct kvm *kvm = vcpu->kvm;
> struct hv_send_ipi_ex send_ipi_ex;
> struct hv_send_ipi send_ipi;
> - DECLARE_BITMAP(vcpu_mask, KVM_MAX_VCPUS);
> unsigned long valid_bank_mask;
> u64 sparse_banks[KVM_HV_MAX_SPARSE_VCPU_SET_BITS];
> u32 vector;
> @@ -2175,13 +2196,7 @@ static u64 kvm_hv_send_ipi(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
> if ((vector < HV_IPI_LOW_VECTOR) || (vector > HV_IPI_HIGH_VECTOR))
> return HV_STATUS_INVALID_HYPERCALL_INPUT;
>
> - if (all_cpus) {
> - kvm_send_ipi_to_many(kvm, vector, NULL);
> - } else {
> - sparse_set_to_vcpu_mask(kvm, sparse_banks, valid_bank_mask, vcpu_mask);
> -
> - kvm_send_ipi_to_many(kvm, vector, vcpu_mask);
> - }
> + kvm_hv_send_ipi_to_many(kvm, vector, all_cpus ? NULL : sparse_banks, valid_bank_mask);
>
> ret_success:
> return HV_STATUS_SUCCESS;

Overall looks good to me, but I might have missed something.

Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>

Best regards,
Maxim Levitsky