KVM: Introduce paravirtualization hints and KVM_HINTS_DEDICATED

This patch introduces kvm_para_has_hint() to query for hints about
the configuration of the guests.  The first hint KVM_HINTS_DEDICATED,
is set if the guest has dedicated physical CPUs for each vCPU (i.e.
pinning and no over-commitment).  This allows optimizing spinlocks
and tells the guest to avoid PV TLB flush.

Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Eduardo Habkost <ehabkost@redhat.com>
Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Radim Krčmář <rkrcmar@redhat.com>

3 files changed, 17 insertions, 2 deletions

diff --git a/arch/x86/include/asm/kvm_para.h b/arch/x86/include/asm/kvm_para.h
index 7b407dda2bd7..3aea2658323a 100644
--- a/arch/x86/include/asm/kvm_para.h
+++ b/arch/x86/include/asm/kvm_para.h
@@ -88,6 +88,7 @@ static inline long kvm_hypercall4(unsigned int nr, unsigned long p1,
 #ifdef CONFIG_KVM_GUEST
 bool kvm_para_available(void);
 unsigned int kvm_arch_para_features(void);
+unsigned int kvm_arch_para_hints(void);
 void kvm_async_pf_task_wait(u32 token, int interrupt_kernel);
 void kvm_async_pf_task_wake(u32 token);
 u32 kvm_read_and_reset_pf_reason(void);
@@ -115,6 +116,11 @@ static inline unsigned int kvm_arch_para_features(void)
 	return 0;
 }
 
+static inline unsigned int kvm_arch_para_hints(void)
+{
+	return 0;
+}
+
 static inline u32 kvm_read_and_reset_pf_reason(void)
 {
 	return 0;
diff --git a/arch/x86/include/uapi/asm/kvm_para.h b/arch/x86/include/uapi/asm/kvm_para.h
index 6cfa9c8cb7d6..68a41b6ba3da 100644
--- a/arch/x86/include/uapi/asm/kvm_para.h
+++ b/arch/x86/include/uapi/asm/kvm_para.h
@@ -10,8 +10,10 @@
  */
 #define KVM_CPUID_SIGNATURE	0x40000000
 
-/* This CPUID returns a feature bitmap in eax.  Before enabling a particular
- * paravirtualization, the appropriate feature bit should be checked.
+/* This CPUID returns two feature bitmaps in eax, edx. Before enabling
+ * a particular paravirtualization, the appropriate feature bit should
+ * be checked in eax. The performance hint feature bit should be checked
+ * in edx.
  */
 #define KVM_CPUID_FEATURES	0x40000001
 #define KVM_FEATURE_CLOCKSOURCE		0
@@ -28,6 +30,8 @@
 #define KVM_FEATURE_PV_TLB_FLUSH	9
 #define KVM_FEATURE_ASYNC_PF_VMEXIT	10
 
+#define KVM_HINTS_DEDICATED      0
+
 /* The last 8 bits are used to indicate how to interpret the flags field
  * in pvclock structure. If no bits are set, all flags are ignored.
  */
diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index bc1a27280c4b..8c9d98c46f84 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -605,6 +605,11 @@ unsigned int kvm_arch_para_features(void)
 	return cpuid_eax(kvm_cpuid_base() | KVM_CPUID_FEATURES);
 }
 
+unsigned int kvm_arch_para_hints(void)
+{
+	return cpuid_edx(kvm_cpuid_base() | KVM_CPUID_FEATURES);
+}
+
 static uint32_t __init kvm_detect(void)
 {
 	return kvm_cpuid_base();