KVM: selftests: Split out kvm_cpuid2_size() from allocate_kvm_cpuid2()

Split out the computation of the effective size of a kvm_cpuid2 struct
from allocate_kvm_cpuid2(), and modify both to take an arbitrary number
of entries.  Future commits will add caching of a vCPU's CPUID model, and
will (a) be able to precisely size the entries array, and (b) will need
to know the effective size of the struct in order to copy to/from the
cache.

Expose the helpers so that the Hyper-V Features test can use them in the
(somewhat distant) future.  The Hyper-V test very, very subtly relies on
propagating CPUID info across vCPU instances, and will need to make a
copy of the previous vCPU's CPUID information when it switches to using
the per-vCPU cache.  Alternatively, KVM could provide helpers to
duplicate and/or copy a kvm_cpuid2 instance, but each is literally a
single line of code if the helpers are exposed, and it's not like the
size of kvm_cpuid2 is secret knowledge.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20220614200707.3315957-18-seanjc@google.com

1 files changed, 23 insertions, 0 deletions

diff --git a/tools/testing/selftests/kvm/include/x86_64/processor.h b/tools/testing/selftests/kvm/include/x86_64/processor.h
index a66d625da3d4..1326377f72b7 100644
--- a/tools/testing/selftests/kvm/include/x86_64/processor.h
+++ b/tools/testing/selftests/kvm/include/x86_64/processor.h
@@ -595,6 +595,29 @@ static inline bool kvm_cpu_has(struct kvm_x86_cpu_feature feature)
 	return kvm_cpuid_has(kvm_get_supported_cpuid(), feature);
 }
 
+static inline size_t kvm_cpuid2_size(int nr_entries)
+{
+	return sizeof(struct kvm_cpuid2) +
+	       sizeof(struct kvm_cpuid_entry2) * nr_entries;
+}
+
+/*
+ * Allocate a "struct kvm_cpuid2* instance, with the 0-length arrary of
+ * entries sized to hold @nr_entries.  The caller is responsible for freeing
+ * the struct.
+ */
+static inline struct kvm_cpuid2 *allocate_kvm_cpuid2(int nr_entries)
+{
+	struct kvm_cpuid2 *cpuid;
+
+	cpuid = malloc(kvm_cpuid2_size(nr_entries));
+	TEST_ASSERT(cpuid, "-ENOMEM when allocating kvm_cpuid2");
+
+	cpuid->nent = nr_entries;
+
+	return cpuid;
+}
+
 struct kvm_cpuid2 *vcpu_get_cpuid(struct kvm_vcpu *vcpu);
 
 static inline int __vcpu_set_cpuid(struct kvm_vcpu *vcpu,