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Date: Mon, 25 Oct 2021 15:31:48 +0200 From: Paolo Bonzini <pbonzini@...hat.com> To: Sean Christopherson <seanjc@...gle.com>, Marc Zyngier <maz@...nel.org>, Huacai Chen <chenhuacai@...nel.org>, Aleksandar Markovic <aleksandar.qemu.devel@...il.com>, Paul Mackerras <paulus@...abs.org>, Anup Patel <anup.patel@....com>, Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>, Christian Borntraeger <borntraeger@...ibm.com>, Janosch Frank <frankja@...ux.ibm.com> Cc: James Morse <james.morse@....com>, Alexandru Elisei <alexandru.elisei@....com>, Suzuki K Poulose <suzuki.poulose@....com>, Atish Patra <atish.patra@....com>, David Hildenbrand <david@...hat.com>, Cornelia Huck <cohuck@...hat.com>, Claudio Imbrenda <imbrenda@...ux.ibm.com>, Vitaly Kuznetsov <vkuznets@...hat.com>, Wanpeng Li <wanpengli@...cent.com>, Jim Mattson <jmattson@...gle.com>, Joerg Roedel <joro@...tes.org>, linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.cs.columbia.edu, linux-mips@...r.kernel.org, kvm@...r.kernel.org, kvm-ppc@...r.kernel.org, kvm-riscv@...ts.infradead.org, linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org, David Matlack <dmatlack@...gle.com>, Oliver Upton <oupton@...gle.com>, Jing Zhang <jingzhangos@...gle.com> Subject: Re: [PATCH v2 10/43] KVM: arm64: Move vGIC v4 handling for WFI out arch callback hook On 09/10/21 04:12, Sean Christopherson wrote: > Move the put and reload of the vGIC out of the block/unblock callbacks > and into a dedicated WFI helper. Functionally, this is nearly a nop as > the block hook is called at the very beginning of kvm_vcpu_block(), and > the only code in kvm_vcpu_block() after the unblock hook is to update the > halt-polling controls, i.e. can only affect the next WFI. > > Back when the arch (un)blocking hooks were added by commits 3217f7c25bca > ("KVM: Add kvm_arch_vcpu_{un}blocking callbacks) and d35268da6687 > ("arm/arm64: KVM: arch_timer: Only schedule soft timer on vcpu_block"), > the hooks were invoked only when KVM was about to "block", i.e. schedule > out the vCPU. The use case at the time was to schedule a timer in the > host based on the earliest timer in the guest in order to wake the > blocking vCPU when the emulated guest timer fired. Commit accb99bcd0ca > ("KVM: arm/arm64: Simplify bg_timer programming") reworked the timer > logic to be even more precise, by waiting until the vCPU was actually > scheduled out, and so move the timer logic from the (un)blocking hooks to > vcpu_load/put. > > In the meantime, the hooks gained usage for enabling vGIC v4 doorbells in > commit df9ba95993b9 ("KVM: arm/arm64: GICv4: Use the doorbell interrupt > as an unblocking source"), and added related logic for the VMCR in commit > 5eeaf10eec39 ("KVM: arm/arm64: Sync ICH_VMCR_EL2 back when about to block"). > > Finally, commit 07ab0f8d9a12 ("KVM: Call kvm_arch_vcpu_blocking early > into the blocking sequence") hoisted the (un)blocking hooks so that they > wrapped KVM's halt-polling logic in addition to the core "block" logic. > > In other words, the original need for arch hooks to take action _only_ > in the block path is long since gone. > > Cc: Oliver Upton <oupton@...gle.com> > Cc: Marc Zyngier <maz@...nel.org> > Signed-off-by: Sean Christopherson <seanjc@...gle.com> This needs a word on why kvm_psci_vcpu_suspend does not need the hooks. Or it needs to be changed to also use kvm_vcpu_wfi in the PSCI code, I don't know. Marc, can you review and/or advise? Thanks, Paolo > --- > arch/arm64/include/asm/kvm_emulate.h | 2 ++ > arch/arm64/kvm/arm.c | 52 +++++++++++++++++++--------- > arch/arm64/kvm/handle_exit.c | 3 +- > 3 files changed, 38 insertions(+), 19 deletions(-) > > diff --git a/arch/arm64/include/asm/kvm_emulate.h b/arch/arm64/include/asm/kvm_emulate.h > index fd418955e31e..de8b4f5922b7 100644 > --- a/arch/arm64/include/asm/kvm_emulate.h > +++ b/arch/arm64/include/asm/kvm_emulate.h > @@ -41,6 +41,8 @@ void kvm_inject_vabt(struct kvm_vcpu *vcpu); > void kvm_inject_dabt(struct kvm_vcpu *vcpu, unsigned long addr); > void kvm_inject_pabt(struct kvm_vcpu *vcpu, unsigned long addr); > > +void kvm_vcpu_wfi(struct kvm_vcpu *vcpu); > + > static __always_inline bool vcpu_el1_is_32bit(struct kvm_vcpu *vcpu) > { > return !(vcpu->arch.hcr_el2 & HCR_RW); > diff --git a/arch/arm64/kvm/arm.c b/arch/arm64/kvm/arm.c > index 7838e9fb693e..1346f81b34df 100644 > --- a/arch/arm64/kvm/arm.c > +++ b/arch/arm64/kvm/arm.c > @@ -359,27 +359,12 @@ int kvm_cpu_has_pending_timer(struct kvm_vcpu *vcpu) > > void kvm_arch_vcpu_blocking(struct kvm_vcpu *vcpu) > { > - /* > - * If we're about to block (most likely because we've just hit a > - * WFI), we need to sync back the state of the GIC CPU interface > - * so that we have the latest PMR and group enables. This ensures > - * that kvm_arch_vcpu_runnable has up-to-date data to decide > - * whether we have pending interrupts. > - * > - * For the same reason, we want to tell GICv4 that we need > - * doorbells to be signalled, should an interrupt become pending. > - */ > - preempt_disable(); > - kvm_vgic_vmcr_sync(vcpu); > - vgic_v4_put(vcpu, true); > - preempt_enable(); > + > } > > void kvm_arch_vcpu_unblocking(struct kvm_vcpu *vcpu) > { > - preempt_disable(); > - vgic_v4_load(vcpu); > - preempt_enable(); > + > } > > void kvm_arch_vcpu_load(struct kvm_vcpu *vcpu, int cpu) > @@ -662,6 +647,39 @@ static void vcpu_req_sleep(struct kvm_vcpu *vcpu) > smp_rmb(); > } > > +/** > + * kvm_vcpu_wfi - emulate Wait-For-Interrupt behavior > + * @vcpu: The VCPU pointer > + * > + * Suspend execution of a vCPU until a valid wake event is detected, i.e. until > + * the vCPU is runnable. The vCPU may or may not be scheduled out, depending > + * on when a wake event arrives, e.g. there may already be a pending wake event. > + */ > +void kvm_vcpu_wfi(struct kvm_vcpu *vcpu) > +{ > + /* > + * Sync back the state of the GIC CPU interface so that we have > + * the latest PMR and group enables. This ensures that > + * kvm_arch_vcpu_runnable has up-to-date data to decide whether > + * we have pending interrupts, e.g. when determining if the > + * vCPU should block. > + * > + * For the same reason, we want to tell GICv4 that we need > + * doorbells to be signalled, should an interrupt become pending. > + */ > + preempt_disable(); > + kvm_vgic_vmcr_sync(vcpu); > + vgic_v4_put(vcpu, true); > + preempt_enable(); > + > + kvm_vcpu_block(vcpu); > + kvm_clear_request(KVM_REQ_UNHALT, vcpu); > + > + preempt_disable(); > + vgic_v4_load(vcpu); > + preempt_enable(); > +} > + > static int kvm_vcpu_initialized(struct kvm_vcpu *vcpu) > { > return vcpu->arch.target >= 0; > diff --git a/arch/arm64/kvm/handle_exit.c b/arch/arm64/kvm/handle_exit.c > index 275a27368a04..4794563a506b 100644 > --- a/arch/arm64/kvm/handle_exit.c > +++ b/arch/arm64/kvm/handle_exit.c > @@ -95,8 +95,7 @@ static int kvm_handle_wfx(struct kvm_vcpu *vcpu) > } else { > trace_kvm_wfx_arm64(*vcpu_pc(vcpu), false); > vcpu->stat.wfi_exit_stat++; > - kvm_vcpu_block(vcpu); > - kvm_clear_request(KVM_REQ_UNHALT, vcpu); > + kvm_vcpu_wfi(vcpu); > } > > kvm_incr_pc(vcpu); >
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