[PATCH AUTOSEL 5.15 10/23] x86/kvm: Don't use pv tlb/ipi/sched_yield if on 1 vCPU

[Sasha Levin]

From: Wanpeng Li <wanpengli@xxxxxxxxxxx>

[ Upstream commit ec756e40e271866f951d77c5e923d8deb6002b15 ]

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@xxxxxxxxxxx>
Message-Id: <1645171838-2855-1-git-send-email-wanpengli@xxxxxxxxxxx>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
 arch/x86/kernel/kvm.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kernel/kvm.c b/arch/x86/kernel/kvm.c
index b656456c3a944..811c7aaf23aac 100644
--- a/arch/x86/kernel/kvm.c
+++ b/arch/x86/kernel/kvm.c
@@ -457,19 +457,22 @@ 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)
-- 
2.34.1