linux-kernel - [PATCH] KVM: LAPIC: Per vCPU control over kvm_can_post_timer

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Message-ID: <20211122095619.000060d2@gmail.com>
Date:   Mon, 22 Nov 2021 09:58:05 +0800
From:   Aili Yao <yaoaili126@...il.com>
To:     pbonzini@...hat.com, seanjc@...gle.com, vkuznets@...hat.com,
        wanpengli@...cent.com, jmattson@...gle.com, joro@...tes.org,
        tglx@...utronix.de, mingo@...hat.com, bp@...en8.de,
        dave.hansen@...ux.intel.com
Cc:     x86@...nel.org, hpa@...or.com, kvm@...r.kernel.org,
        linux-kernel@...r.kernel.org, yaoaili@...gsoft.com
Subject: [PATCH] KVM: LAPIC: Per vCPU control over
 kvm_can_post_timer_interrupt

From: Aili Yao <yaoaili@...gsoft.com>

When we isolate some pyhiscal cores, We may not use them for kvm guests,
We may use them for other purposes like DPDK, or we can make some kvm
guests isolated and some not, the global judgement pi_inject_timer is
not enough; We may make wrong decisions:

In such a scenario, the guests without isolated cores will not be
permitted to use vmx preemption timer, and tscdeadline fastpath also be
disabled, both will lead to performance penalty.

So check whether the vcpu->cpu is isolated, if not, don't post timer
interrupt.

Signed-off-by: Aili Yao <yaoaili@...gsoft.com>
---
 arch/x86/kvm/lapic.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 759952dd1222..72dde5532101 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -34,6 +34,7 @@
 #include <asm/delay.h>
 #include <linux/atomic.h>
 #include <linux/jump_label.h>
+#include <linux/sched/isolation.h>
 #include "kvm_cache_regs.h"
 #include "irq.h"
 #include "ioapic.h"
@@ -113,7 +114,8 @@ 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_vcpu_apicv_active(vcpu) &&
+		!housekeeping_cpu(vcpu->cpu, HK_FLAG_TIMER);
 }
 
 bool kvm_can_use_hv_timer(struct kvm_vcpu *vcpu)
-- 
2.25.1