Re: [PATCH v2 2/2] KVM: arm64: Delay the execution of the polling on the GICR_VPENDBASER.Dirty bit

[Marc Zyngier <maz@kernel.org>]

On 2020-11-28 14:18, Shenming Lu wrote:
> In order to further reduce the impact of the wait delay of the
> VPT analysis, we can delay the execution of the polling on the
> GICR_VPENDBASER.Dirty bit (call it from kvm_vgic_flush_hwstate()
> corresponding to vPE resident), let the GIC and the CPU work in
> parallel on the entry path.
> 
> Signed-off-by: Shenming Lu <lushenming@huawei.com>
> ---
>  arch/arm64/kvm/vgic/vgic-v4.c      | 16 ++++++++++++++++
>  arch/arm64/kvm/vgic/vgic.c         |  3 +++
>  drivers/irqchip/irq-gic-v3-its.c   | 16 ++++++++++++----
>  drivers/irqchip/irq-gic-v4.c       | 11 +++++++++++
>  include/kvm/arm_vgic.h             |  3 +++
>  include/linux/irqchip/arm-gic-v4.h |  4 ++++
>  6 files changed, 49 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/arm64/kvm/vgic/vgic-v4.c 
> b/arch/arm64/kvm/vgic/vgic-v4.c
> index b5fa73c9fd35..b0da74809187 100644
> --- a/arch/arm64/kvm/vgic/vgic-v4.c
> +++ b/arch/arm64/kvm/vgic/vgic-v4.c
> @@ -353,6 +353,22 @@ int vgic_v4_load(struct kvm_vcpu *vcpu)
>  	return err;
>  }
> 
> +void vgic_v4_commit(struct kvm_vcpu *vcpu)
> +{
> +	struct its_vpe *vpe = &vcpu->arch.vgic_cpu.vgic_v3.its_vpe;
> +
> +	/*
> +	 * No need to wait for the vPE to be ready across a shallow guest
> +	 * exit, as only a vcpu_put will invalidate it.
> +	 */
> +	if (vpe->vpe_ready)
> +		return;
> +
> +	its_commit_vpe(vpe);
> +
> +	vpe->vpe_ready = true;

This should be written as:

if (!ready)
      commit();

and ready being driven by the commit() call itself.

> +}
> +
>  static struct vgic_its *vgic_get_its(struct kvm *kvm,
>  				     struct kvm_kernel_irq_routing_entry *irq_entry)
>  {
> diff --git a/arch/arm64/kvm/vgic/vgic.c b/arch/arm64/kvm/vgic/vgic.c
> index c3643b7f101b..1c597c9885fa 100644
> --- a/arch/arm64/kvm/vgic/vgic.c
> +++ b/arch/arm64/kvm/vgic/vgic.c
> @@ -915,6 +915,9 @@ void kvm_vgic_flush_hwstate(struct kvm_vcpu *vcpu)
> 
>  	if (can_access_vgic_from_kernel())
>  		vgic_restore_state(vcpu);
> +
> +	if (vgic_supports_direct_msis(vcpu->kvm))
> +		vgic_v4_commit(vcpu);
>  }
> 
>  void kvm_vgic_load(struct kvm_vcpu *vcpu)
> diff --git a/drivers/irqchip/irq-gic-v3-its.c 
> b/drivers/irqchip/irq-gic-v3-its.c
> index 22f427135c6b..f30aba14933e 100644
> --- a/drivers/irqchip/irq-gic-v3-its.c
> +++ b/drivers/irqchip/irq-gic-v3-its.c
> @@ -3842,8 +3842,6 @@ static void its_vpe_schedule(struct its_vpe *vpe)
>  	val |= vpe->idai ? GICR_VPENDBASER_IDAI : 0;
>  	val |= GICR_VPENDBASER_Valid;
>  	gicr_write_vpendbaser(val, vlpi_base + GICR_VPENDBASER);
> -
> -	its_wait_vpt_parse_complete();
>  }
> 
>  static void its_vpe_deschedule(struct its_vpe *vpe)
> @@ -3855,6 +3853,8 @@ static void its_vpe_deschedule(struct its_vpe 
> *vpe)
> 
>  	vpe->idai = !!(val & GICR_VPENDBASER_IDAI);
>  	vpe->pending_last = !!(val & GICR_VPENDBASER_PendingLast);
> +
> +	vpe->vpe_ready = false;

This should be set from the its_make_vpe_non_resident() call.

>  }
> 
>  static void its_vpe_invall(struct its_vpe *vpe)
> @@ -3891,6 +3891,10 @@ static int its_vpe_set_vcpu_affinity(struct
> irq_data *d, void *vcpu_info)
>  		its_vpe_deschedule(vpe);
>  		return 0;
> 
> +	case COMMIT_VPE:
> +		its_wait_vpt_parse_complete();
> +		return 0;
> +
>  	case INVALL_VPE:
>  		its_vpe_invall(vpe);
>  		return 0;
> @@ -4052,8 +4056,6 @@ static void its_vpe_4_1_schedule(struct its_vpe 
> *vpe,
>  	val |= FIELD_PREP(GICR_VPENDBASER_4_1_VPEID, vpe->vpe_id);
> 
>  	gicr_write_vpendbaser(val, vlpi_base + GICR_VPENDBASER);
> -
> -	its_wait_vpt_parse_complete();
>  }
> 
>  static void its_vpe_4_1_deschedule(struct its_vpe *vpe,
> @@ -4091,6 +4093,8 @@ static void its_vpe_4_1_deschedule(struct its_vpe 
> *vpe,
>  					    GICR_VPENDBASER_PendingLast);
>  		vpe->pending_last = true;
>  	}
> +
> +	vpe->vpe_ready = false;
>  }
> 
>  static void its_vpe_4_1_invall(struct its_vpe *vpe)
> @@ -4128,6 +4132,10 @@ static int its_vpe_4_1_set_vcpu_affinity(struct
> irq_data *d, void *vcpu_info)
>  		its_vpe_4_1_deschedule(vpe, info);
>  		return 0;
> 
> +	case COMMIT_VPE:
> +		its_wait_vpt_parse_complete();
> +		return 0;
> +
>  	case INVALL_VPE:
>  		its_vpe_4_1_invall(vpe);
>  		return 0;
> diff --git a/drivers/irqchip/irq-gic-v4.c 
> b/drivers/irqchip/irq-gic-v4.c
> index 0c18714ae13e..6cea71a4e68b 100644
> --- a/drivers/irqchip/irq-gic-v4.c
> +++ b/drivers/irqchip/irq-gic-v4.c
> @@ -258,6 +258,17 @@ int its_make_vpe_resident(struct its_vpe *vpe,
> bool g0en, bool g1en)
>  	return ret;
>  }
> 
> +int its_commit_vpe(struct its_vpe *vpe)
> +{
> +	struct its_cmd_info info = {
> +		.cmd_type = COMMIT_VPE,
> +	};
> +
> +	WARN_ON(preemptible());
> +
> +	return its_send_vpe_cmd(vpe, &info);
> +}
> +
>  int its_invall_vpe(struct its_vpe *vpe)
>  {
>  	struct its_cmd_info info = {
> diff --git a/include/kvm/arm_vgic.h b/include/kvm/arm_vgic.h
> index a8d8fdcd3723..f2170df6cf7c 100644
> --- a/include/kvm/arm_vgic.h
> +++ b/include/kvm/arm_vgic.h
> @@ -401,7 +401,10 @@ int kvm_vgic_v4_set_forwarding(struct kvm *kvm, 
> int irq,
>  int kvm_vgic_v4_unset_forwarding(struct kvm *kvm, int irq,
>  				 struct kvm_kernel_irq_routing_entry *irq_entry);
> 
> +void vgic_v4_commit(struct kvm_vcpu *vcpu);
> +
>  int vgic_v4_load(struct kvm_vcpu *vcpu);
> +

Spurious new lines.

>  int vgic_v4_put(struct kvm_vcpu *vcpu, bool need_db);
> 
>  #endif /* __KVM_ARM_VGIC_H */
> diff --git a/include/linux/irqchip/arm-gic-v4.h
> b/include/linux/irqchip/arm-gic-v4.h
> index 6976b8331b60..936d88e482a9 100644
> --- a/include/linux/irqchip/arm-gic-v4.h
> +++ b/include/linux/irqchip/arm-gic-v4.h
> @@ -75,6 +75,8 @@ struct its_vpe {
>  	u16			vpe_id;
>  	/* Pending VLPIs on schedule out? */
>  	bool			pending_last;
> +	/* VPT parse complete */
> +	bool			vpe_ready;
>  };
> 
>  /*
> @@ -104,6 +106,7 @@ enum its_vcpu_info_cmd_type {
>  	PROP_UPDATE_AND_INV_VLPI,
>  	SCHEDULE_VPE,
>  	DESCHEDULE_VPE,
> +	COMMIT_VPE,
>  	INVALL_VPE,
>  	PROP_UPDATE_VSGI,
>  };
> @@ -129,6 +132,7 @@ int its_alloc_vcpu_irqs(struct its_vm *vm);
>  void its_free_vcpu_irqs(struct its_vm *vm);
>  int its_make_vpe_resident(struct its_vpe *vpe, bool g0en, bool g1en);
>  int its_make_vpe_non_resident(struct its_vpe *vpe, bool db);
> +int its_commit_vpe(struct its_vpe *vpe);
>  int its_invall_vpe(struct its_vpe *vpe);
>  int its_map_vlpi(int irq, struct its_vlpi_map *map);
>  int its_get_vlpi(int irq, struct its_vlpi_map *map);

In order to speed up the respin round-trip, I've taken the liberty
to refactor this patch myself. Please have a look at [1] and let
me know if you're OK with it.

Thanks,

         M.

[1] 
https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms.git/commit/?h=kvm-arm64/misc-5.11&id=57e3cebd022fbc035dcf190ac789fd2ffc747f5b
-- 
Jazz is not dead. It just smells funny...

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