linux-kernel - [PATCH] KVM: LAPIC: To keep the vCPUs in non-root mode for timer-pi

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Date:   Tue, 23 Nov 2021 21:59:45 -0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>,
        Vitaly Kuznetsov <vkuznets@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>, Aili Yao <yaoaili@...gsoft.com>
Subject: [PATCH] KVM: LAPIC: To keep the vCPUs in non-root mode for timer-pi

From: Wanpeng Li <wanpengli@...cent.com>

As commit 0c5f81dad46 (KVM: LAPIC: Inject timer interrupt via posted interrupt) 
mentioned that the host admin should well tune the guest setup, so that vCPUs 
are placed on isolated pCPUs, and with several pCPUs surplus for *busy* housekeeping.
It is better to disable mwait/hlt/pause vmexits to keep the vCPUs in non-root 
mode. However, we may isolate pCPUs for other purpose like DPDK or we can make 
some guests isolated and others not, Let's add the checking kvm_mwait_in_guest() 
to kvm_can_post_timer_interrupt() since we can't benefit from timer posted-interrupt 
w/o keeping the vCPUs in non-root mode.

Reported-by: Aili Yao <yaoaili@...gsoft.com>
Cc: Aili Yao <yaoaili@...gsoft.com>
Signed-off-by: Wanpeng Li <wanpengli@...cent.com>
---
 arch/x86/kvm/lapic.c | 5 ++---
 1 file changed, 2 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 759952dd1222..8257566d44c7 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -113,14 +113,13 @@ static inline u32 kvm_x2apic_id(struct kvm_lapic *apic)
 
 static bool kvm_can_post_timer_interrupt(struct kvm_vcpu *vcpu)
 {
-	return pi_inject_timer && kvm_vcpu_apicv_active(vcpu);
+	return pi_inject_timer && kvm_mwait_in_guest(vcpu->kvm) && kvm_vcpu_apicv_active(vcpu);
 }
 
 bool kvm_can_use_hv_timer(struct kvm_vcpu *vcpu)
 {
 	return kvm_x86_ops.set_hv_timer
-	       && !(kvm_mwait_in_guest(vcpu->kvm) ||
-		    kvm_can_post_timer_interrupt(vcpu));
+	       && !kvm_mwait_in_guest(vcpu->kvm);
 }
 EXPORT_SYMBOL_GPL(kvm_can_use_hv_timer);
 
-- 
2.25.1