Re: [PATCH v7 10/39] KVM: x86: hyper-v: Don't use sparse_set_to_vcpu_mask() in kvm_hv_send_ipi()

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On 6/13/22 15:38, 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.

Reviewed-by: Maxim Levitsky <mlevitsk@xxxxxxxxxx>
Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>
---
  arch/x86/kvm/hyperv.c | 37 ++++++++++++++++++++++++++-----------
  1 file changed, 26 insertions(+), 11 deletions(-)

I'm a bit confused by this patch being in this series.

Just to be clear, PV IPI does *not* support the VP_ID, right? And since patch 12 only affects the sparse banks, the patch does not have any other dependency. Is this correct?

Paolo

diff --git a/arch/x86/kvm/hyperv.c b/arch/x86/kvm/hyperv.c
index f41153c71beb..269a5fcca31b 100644
--- a/arch/x86/kvm/hyperv.c
+++ b/arch/x86/kvm/hyperv.c
@@ -1747,6 +1747,25 @@ 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;
@@ -2029,8 +2048,8 @@ 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)
  {
  	struct kvm_lapic_irq irq = {
  		.delivery_mode = APIC_DM_FIXED,
@@ -2040,7 +2059,10 @@ 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 */
@@ -2053,7 +2075,6 @@ 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);
  	u64 valid_bank_mask;
  	u64 sparse_banks[KVM_HV_MAX_SPARSE_VCPU_SET_BITS];
  	u32 vector;
@@ -2115,13 +2136,7 @@ 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;




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