On 4/27/22 17:54, Sasha Levin wrote:
From: Wanpeng Li wanpengli@tencent.com
[ Upstream commit 1714a4eb6fb0cb79f182873cd011a8ed60ac65e8 ]
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. In this setup, it is preferrable to disable mwait/hlt/pause vmexits to keep the vCPUs in non-root mode.
However, if only some guests isolated and others not, they would not have any benefit from posted timer interrupts, and at the same time lose VMX preemption timer fast paths because kvm_can_post_timer_interrupt() returns true and therefore forces kvm_can_use_hv_timer() to false.
By guaranteeing that posted-interrupt timer is only used if MWAIT or HLT are done without vmexit, KVM can make a better choice and use the VMX preemption timer and the corresponding fast paths.
Reported-by: Aili Yao yaoaili@kingsoft.com Reviewed-by: Sean Christopherson seanjc@google.com Cc: Aili Yao yaoaili@kingsoft.com Cc: Sean Christopherson seanjc@google.com Signed-off-by: Wanpeng Li wanpengli@tencent.com Message-Id: 1643112538-36743-1-git-send-email-wanpengli@tencent.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org
arch/x86/kvm/lapic.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c index e45ebf0870b6..a3ef793fce5f 100644 --- a/arch/x86/kvm/lapic.c +++ b/arch/x86/kvm/lapic.c @@ -113,7 +113,8 @@ 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) &&
(kvm_mwait_in_guest(vcpu->kvm) || kvm_hlt_in_guest(vcpu->kvm));bool kvm_can_use_hv_timer(struct kvm_vcpu *vcpu)
Acked-by: Paolo Bonzini pbonzini@redhat.com