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bh=F4tMjT47BZ3DwbmAEWq81W0GAGbuRTe5m3IotIof8YU=; b=BjqOJFROTIOhDmJkCsO6Exs79jec8AvAq0YcQV3+y6zihBb/DGdQas3lnaz5aNxZE2hqbK WhObPml9ixi3GkAgkTvb2ovSasE+MsFT1a5iP4142pp+zyc0PR58hxt5QbukfE3NmyqktO zLewA7VN5IUax5mM4WnTFZ7PBNDdWt8= Received: from mimecast-mx01.redhat.com (mimecast-mx01.redhat.com [209.132.183.4]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-192-HPiuQd71NyeJUfJbOWNqdw-1; Thu, 28 Oct 2021 11:46:07 -0400 X-MC-Unique: HPiuQd71NyeJUfJbOWNqdw-1 Received: from smtp.corp.redhat.com (int-mx04.intmail.prod.int.phx2.redhat.com [10.5.11.14]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx01.redhat.com (Postfix) with ESMTPS id F02CB19251A0; Thu, 28 Oct 2021 15:46:02 +0000 (UTC) Received: from starship (unknown [10.40.194.243]) by smtp.corp.redhat.com (Postfix) with ESMTP id 9106C5DA61; Thu, 28 Oct 2021 15:45:15 +0000 (UTC) Message-ID: <06ed37a510347fdc7c6f7ce46fd98ce5b9ff7554.camel@redhat.com> Subject: Re: [PATCH v2 32/43] KVM: VMX: Move preemption timer <=> hrtimer dance to common x86 From: Maxim Levitsky To: Sean Christopherson , Marc Zyngier , Huacai Chen , Aleksandar Markovic , Paul Mackerras , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Christian Borntraeger , Janosch Frank , Paolo Bonzini Cc: James Morse , Alexandru Elisei , Suzuki K Poulose , Atish Patra , David Hildenbrand , Cornelia Huck , Claudio Imbrenda , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-mips@vger.kernel.org, kvm@vger.kernel.org, kvm-ppc@vger.kernel.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, David Matlack , Oliver Upton , Jing Zhang Date: Thu, 28 Oct 2021 18:45:14 +0300 In-Reply-To: <20211009021236.4122790-33-seanjc@google.com> References: <20211009021236.4122790-1-seanjc@google.com> <20211009021236.4122790-33-seanjc@google.com> User-Agent: Evolution 3.36.5 (3.36.5-2.fc32) MIME-Version: 1.0 X-Scanned-By: MIMEDefang 2.79 on 10.5.11.14 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20211028_084611_769792_E03DE8FE X-CRM114-Status: GOOD ( 28.87 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org On Fri, 2021-10-08 at 19:12 -0700, Sean Christopherson wrote: > Handle the switch to/from the hypervisor/software timer when a vCPU is > blocking in common x86 instead of in VMX. Even though VMX is the only > user of a hypervisor timer, the logic and all functions involved are > generic x86 (unless future CPUs do something completely different and > implement a hypervisor timer that runs regardless of mode). > > Handling the switch in common x86 will allow for the elimination of the > pre/post_blocks hooks, and also lets KVM switch back to the hypervisor > timer if and only if it was in use (without additional params). Add a > comment explaining why the switch cannot be deferred to kvm_sched_out() > or kvm_vcpu_block(). > > Signed-off-by: Sean Christopherson > --- > arch/x86/kvm/vmx/vmx.c | 6 +----- > arch/x86/kvm/x86.c | 21 +++++++++++++++++++++ > 2 files changed, 22 insertions(+), 5 deletions(-) > > diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c > index b3bb2031a7ac..a24f19874716 100644 > --- a/arch/x86/kvm/vmx/vmx.c > +++ b/arch/x86/kvm/vmx/vmx.c > @@ -7464,16 +7464,12 @@ void vmx_update_cpu_dirty_logging(struct kvm_vcpu *vcpu) > > static int vmx_pre_block(struct kvm_vcpu *vcpu) > { > - if (kvm_lapic_hv_timer_in_use(vcpu)) > - kvm_lapic_switch_to_sw_timer(vcpu); > - > return 0; > } > > static void vmx_post_block(struct kvm_vcpu *vcpu) > { > - if (kvm_x86_ops.set_hv_timer) > - kvm_lapic_switch_to_hv_timer(vcpu); > + > } > > static void vmx_setup_mce(struct kvm_vcpu *vcpu) > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index e0219acfd9cf..909e932a7ae7 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -9896,8 +9896,21 @@ static int vcpu_enter_guest(struct kvm_vcpu *vcpu) > > static inline int vcpu_block(struct kvm *kvm, struct kvm_vcpu *vcpu) > { > + bool hv_timer; > + > if (!kvm_arch_vcpu_runnable(vcpu) && > (!kvm_x86_ops.pre_block || static_call(kvm_x86_pre_block)(vcpu) == 0)) { > + /* > + * Switch to the software timer before halt-polling/blocking as > + * the guest's timer may be a break event for the vCPU, and the > + * hypervisor timer runs only when the CPU is in guest mode. > + * Switch before halt-polling so that KVM recognizes an expired > + * timer before blocking. > + */ I didn't knew about this until now but it all makes sense. The comment is very good. > + hv_timer = kvm_lapic_hv_timer_in_use(vcpu); > + if (hv_timer) > + kvm_lapic_switch_to_sw_timer(vcpu); > + > srcu_read_unlock(&kvm->srcu, vcpu->srcu_idx); > if (vcpu->arch.mp_state == KVM_MP_STATE_HALTED) > kvm_vcpu_halt(vcpu); > @@ -9905,6 +9918,9 @@ static inline int vcpu_block(struct kvm *kvm, struct kvm_vcpu *vcpu) > kvm_vcpu_block(vcpu); > vcpu->srcu_idx = srcu_read_lock(&kvm->srcu); > > + if (hv_timer) > + kvm_lapic_switch_to_hv_timer(vcpu); > + > if (kvm_x86_ops.post_block) > static_call(kvm_x86_post_block)(vcpu); > > @@ -10136,6 +10152,11 @@ int kvm_arch_vcpu_ioctl_run(struct kvm_vcpu *vcpu) > r = -EINTR; > goto out; > } > + /* > + * It should be impossible for the hypervisor timer to be in > + * use before KVM has ever run the vCPU. > + */ > + WARN_ON_ONCE(kvm_lapic_hv_timer_in_use(vcpu)); > kvm_vcpu_block(vcpu); > if (kvm_apic_accept_events(vcpu) < 0) { > r = 0; Reviewed-by: Maxim Levitsky Best regards, Maxim Levitsky _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv