x86/kvm: Don't use pv tlb/ipi/sched_yield if on 1 vCPU

Inspired by commit 3553ae5690a (x86/kvm: Don't use pvqspinlock code if
only 1 vCPU), on a VM with only 1 vCPU, there is no need to enable
pv tlb/ipi/sched_yield and we can save the memory for __pv_cpu_mask.

Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
Message-Id: <1645171838-2855-1-git-send-email-wanpengli@tencent.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index a438217..f734e3b 100644 (file)
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -462,19 +462,22 @@ static bool pv_tlb_flush_supported(void)
 {
        return (kvm_para_has_feature(KVM_FEATURE_PV_TLB_FLUSH) &&
                !kvm_para_has_hint(KVM_HINTS_REALTIME) &&
-               kvm_para_has_feature(KVM_FEATURE_STEAL_TIME));
+               kvm_para_has_feature(KVM_FEATURE_STEAL_TIME) &&
+               (num_possible_cpus() != 1));
 }
 
 static bool pv_ipi_supported(void)
 {
-       return kvm_para_has_feature(KVM_FEATURE_PV_SEND_IPI);
+       return (kvm_para_has_feature(KVM_FEATURE_PV_SEND_IPI) &&
+              (num_possible_cpus() != 1));
 }
 
 static bool pv_sched_yield_supported(void)
 {
        return (kvm_para_has_feature(KVM_FEATURE_PV_SCHED_YIELD) &&
                !kvm_para_has_hint(KVM_HINTS_REALTIME) &&
-           kvm_para_has_feature(KVM_FEATURE_STEAL_TIME));
+           kvm_para_has_feature(KVM_FEATURE_STEAL_TIME) &&
+           (num_possible_cpus() != 1));
 }
 
 #define KVM_IPI_CLUSTER_SIZE   (2 * BITS_PER_LONG)