KVM: x86: cache maxphyaddr CPUID leaf in struct kvm_vcpu

cpuid_maxphyaddr(), which performs lot of memory accesses is called
extensively across KVM, especially in nVMX code.

This patch adds a cached value of maxphyaddr to vcpu.arch to reduce the
pressure onto CPU cache and simplify the code of cpuid_maxphyaddr()
callers. The cached value is initialized in kvm_arch_vcpu_init() and
reloaded every time CPUID is updated by usermode. It is obvious that
these reloads occur infrequently.

Signed-off-by: Eugene Korenevsky <ekorenevsky@gmail.com>
Message-Id: <20150329205612.GA1223@gnote>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

arch/x86/include/asm/kvm_host.h

@@ -426,6 +426,9 @@ struct kvm_vcpu_arch {
 
 	int cpuid_nent;
 	struct kvm_cpuid_entry2 cpuid_entries[KVM_MAX_CPUID_ENTRIES];
+
+	int maxphyaddr;
+
 	/* emulate context */
 
 	struct x86_emulate_ctxt emulate_ctxt;
@@ -1124,7 +1127,6 @@ int kvm_unmap_hva_range(struct kvm *kvm, unsigned long start, unsigned long end)
 int kvm_age_hva(struct kvm *kvm, unsigned long start, unsigned long end);
 int kvm_test_age_hva(struct kvm *kvm, unsigned long hva);
 void kvm_set_spte_hva(struct kvm *kvm, unsigned long hva, pte_t pte);
-int cpuid_maxphyaddr(struct kvm_vcpu *vcpu);
 int kvm_cpu_has_injectable_intr(struct kvm_vcpu *v);
 int kvm_cpu_has_interrupt(struct kvm_vcpu *vcpu);
 int kvm_arch_interrupt_allowed(struct kvm_vcpu *vcpu);

arch/x86/kvm/cpuid.c

@@ -104,6 +104,9 @@ int kvm_update_cpuid(struct kvm_vcpu *vcpu)
 		((best->eax & 0xff00) >> 8) != 0)
 		return -EINVAL;
 
+	/* Update physical-address width */
+	vcpu->arch.maxphyaddr = cpuid_query_maxphyaddr(vcpu);
+
 	kvm_pmu_cpuid_update(vcpu);
 	return 0;
 }
@@ -135,6 +138,21 @@ static void cpuid_fix_nx_cap(struct kvm_vcpu *vcpu)
 	}
 }
 
+int cpuid_query_maxphyaddr(struct kvm_vcpu *vcpu)
+{
+	struct kvm_cpuid_entry2 *best;
+
+	best = kvm_find_cpuid_entry(vcpu, 0x80000000, 0);
+	if (!best || best->eax < 0x80000008)
+		goto not_found;
+	best = kvm_find_cpuid_entry(vcpu, 0x80000008, 0);
+	if (best)
+		return best->eax & 0xff;
+not_found:
+	return 36;
+}
+EXPORT_SYMBOL_GPL(cpuid_query_maxphyaddr);
+
 /* when an old userspace process fills a new kernel module */
 int kvm_vcpu_ioctl_set_cpuid(struct kvm_vcpu *vcpu,
 			     struct kvm_cpuid *cpuid,
@@ -757,21 +775,6 @@ struct kvm_cpuid_entry2 *kvm_find_cpuid_entry(struct kvm_vcpu *vcpu,
 }
 EXPORT_SYMBOL_GPL(kvm_find_cpuid_entry);
 
-int cpuid_maxphyaddr(struct kvm_vcpu *vcpu)
-{
-	struct kvm_cpuid_entry2 *best;
-
-	best = kvm_find_cpuid_entry(vcpu, 0x80000000, 0);
-	if (!best || best->eax < 0x80000008)
-		goto not_found;
-	best = kvm_find_cpuid_entry(vcpu, 0x80000008, 0);
-	if (best)
-		return best->eax & 0xff;
-not_found:
-	return 36;
-}
-EXPORT_SYMBOL_GPL(cpuid_maxphyaddr);
-
 /*
  * If no match is found, check whether we exceed the vCPU's limit
  * and return the content of the highest valid _standard_ leaf instead.

arch/x86/kvm/cpuid.h

@@ -20,6 +20,12 @@ int kvm_vcpu_ioctl_get_cpuid2(struct kvm_vcpu *vcpu,
 			      struct kvm_cpuid_entry2 __user *entries);
 void kvm_cpuid(struct kvm_vcpu *vcpu, u32 *eax, u32 *ebx, u32 *ecx, u32 *edx);
 
+int cpuid_query_maxphyaddr(struct kvm_vcpu *vcpu);
+
+static inline int cpuid_maxphyaddr(struct kvm_vcpu *vcpu)
+{
+	return vcpu->arch.maxphyaddr;
+}
 
 static inline bool guest_cpuid_has_xsave(struct kvm_vcpu *vcpu)
 {

arch/x86/kvm/x86.c

@@ -7317,6 +7317,8 @@ int kvm_arch_vcpu_init(struct kvm_vcpu *vcpu)
 	vcpu->arch.guest_supported_xcr0 = 0;
 	vcpu->arch.guest_xstate_size = XSAVE_HDR_SIZE + XSAVE_HDR_OFFSET;
 
+	vcpu->arch.maxphyaddr = cpuid_query_maxphyaddr(vcpu);
+
 	kvm_async_pf_hash_reset(vcpu);
 	kvm_pmu_init(vcpu);