KVM: x86: hyper-v: Use preallocated buffer in 'struct kvm_vcpu_hv' instead of...

KVM: x86: hyper-v: Use preallocated buffer in 'struct kvm_vcpu_hv' instead of on-stack 'sparse_banks'

To make kvm_hv_flush_tlb() ready to handle L2 TLB flush requests, KVM needs
to allow for all 64 sparse vCPU banks regardless of KVM_MAX_VCPUs as L1
may use vCPU overcommit for L2. To avoid growing on-stack allocation, make
'sparse_banks' part of per-vCPU 'struct kvm_vcpu_hv' which is allocated
dynamically.

Note: sparse_set_to_vcpu_mask() can't currently be used to handle L2
requests as KVM does not keep L2 VM_ID -> L2 VCPU_ID -> L1 vCPU mappings,
i.e. its vp_bitmap array is still bounded by the number of L1 vCPUs and so
can remain an on-stack allocation.
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20221101145426.251680-19-vkuznets@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -665,6 +665,9 @@ struct kvm_vcpu_hv {
 	} cpuid_cache;
 
 	struct kvm_vcpu_hv_tlb_flush_fifo tlb_flush_fifo[HV_NR_TLB_FLUSH_FIFOS];
+
+	/* Preallocated buffer for handling hypercalls passing sparse vCPU set */
+	u64 sparse_banks[HV_MAX_SPARSE_VCPU_BANKS];
 };
 
 /* Xen HVM per vcpu emulation context */

arch/x86/kvm/hyperv.c

@@ -1906,6 +1906,8 @@ int kvm_hv_vcpu_flush_tlb(struct kvm_vcpu *vcpu)
 
 static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
 {
+	struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
+	u64 *sparse_banks = hv_vcpu->sparse_banks;
 	struct kvm *kvm = vcpu->kvm;
 	struct hv_tlb_flush_ex flush_ex;
 	struct hv_tlb_flush flush;
@@ -1919,7 +1921,6 @@ static u64 kvm_hv_flush_tlb(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
 	u64 __tlb_flush_entries[KVM_HV_TLB_FLUSH_FIFO_SIZE - 1];
 	u64 *tlb_flush_entries;
 	u64 valid_bank_mask;
-	u64 sparse_banks[KVM_HV_MAX_SPARSE_VCPU_SET_BITS];
 	struct kvm_vcpu *v;
 	unsigned long i;
 	bool all_cpus;
@@ -2083,11 +2084,12 @@ static void kvm_hv_send_ipi_to_many(struct kvm *kvm, u32 vector,
 
 static u64 kvm_hv_send_ipi(struct kvm_vcpu *vcpu, struct kvm_hv_hcall *hc)
 {
+	struct kvm_vcpu_hv *hv_vcpu = to_hv_vcpu(vcpu);
+	u64 *sparse_banks = hv_vcpu->sparse_banks;
 	struct kvm *kvm = vcpu->kvm;
 	struct hv_send_ipi_ex send_ipi_ex;
 	struct hv_send_ipi send_ipi;
 	u64 valid_bank_mask;
-	u64 sparse_banks[KVM_HV_MAX_SPARSE_VCPU_SET_BITS];
 	u32 vector;
 	bool all_cpus;