KVM: x86: optimization: cache physical address width to avoid excessive enumerations of CPUID entries

cpuid_maxphyaddr() which performs lot of memory accesses is called extensively across KVM, especially in nVMX code.
This patch adds 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 <[email protected]>

---
 arch/x86/include/asm/kvm_host.h |  4 +++-
 arch/x86/kvm/cpuid.c            | 33 ++++++++++++++++++---------------
 arch/x86/kvm/cpuid.h            |  6 ++++++
 arch/x86/kvm/x86.c              |  2 ++
 4 files changed, 29 insertions(+), 16 deletions(-)

arch/x86/include/asm/kvm_host.h +3 -1

index a236e39..2362a60 100644
@@ -431,6 +431,9 @@ 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;

@@ -1128,7 +1131,6 @@ 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 +18 -15

index 8a80737..59b69f6 100644
@@ -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 +6 -0

index 4452eed..78b61b4 100644
@@ -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 +0 -0

index bd7a70b..084e1d5 100644