Re: [PATCH v5 20/23] KVM: arm64: GICv4.1: Plumb SGI implementation selection in the distributor

[Zenghui Yu]

Hi Marc,

On 2020/3/5 4:33, Marc Zyngier wrote:
> The GICv4.1 architecture gives the hypervisor the option to let
> the guest choose whether it wants the good old SGIs with an
> active state, or the new, HW-based ones that do not have one.
>
> For this, plumb the configuration of SGIs into the GICv3 MMIO
> handling, present the GICD_TYPER2.nASSGIcap to the guest,
> and handle the GICD_CTLR.nASSGIreq setting.
>
> In order to be able to deal with the restore of a guest, also
> apply the GICD_CTLR.nASSGIreq setting at first run so that we
> can move the restored SGIs to the HW if that's what the guest
> had selected in a previous life.

I'm okay with the restore path.  But it seems that we still fail to
save the pending state of vSGI - software pending_latch of HW-based
vSGIs will not be updated (and always be false) because we directly
inject them through ITS, so vgic_v3_uaccess_read_pending() can't
tell the correct pending state to user-space (the correct one should
be latched in HW).

It would be good if we can sync the hardware state into pending_latch
at an appropriate time (just before save), but not sure if we can...

> Signed-off-by: Marc Zyngier <maz@xxxxxxxxxx>
> ---
>   virt/kvm/arm/vgic/vgic-mmio-v3.c | 48 ++++++++++++++++++++++++++++++--
>   virt/kvm/arm/vgic/vgic-v3.c      |  2 ++
>   2 files changed, 48 insertions(+), 2 deletions(-)
>
> diff --git a/virt/kvm/arm/vgic/vgic-mmio-v3.c b/virt/kvm/arm/vgic/vgic-mmio-v3.c
> index de89da76a379..442f3b8c2559 100644
> --- a/virt/kvm/arm/vgic/vgic-mmio-v3.c
> +++ b/virt/kvm/arm/vgic/vgic-mmio-v3.c
> @@ -3,6 +3,7 @@
>    * VGICv3 MMIO handling functions
>    */
>   
> +#include <linux/bitfield.h>
>   #include <linux/irqchip/arm-gic-v3.h>
>   #include <linux/kvm.h>
>   #include <linux/kvm_host.h>
> @@ -70,6 +71,8 @@ static unsigned long vgic_mmio_read_v3_misc(struct kvm_vcpu *vcpu,
>   		if (vgic->enabled)
>   			value |= GICD_CTLR_ENABLE_SS_G1;
>   		value |= GICD_CTLR_ARE_NS | GICD_CTLR_DS;
> +		if (kvm_vgic_global_state.has_gicv4_1 && vgic->nassgireq)

Looking at how we handle the GICD_CTLR.nASSGIreq setting, I think
"nassgireq==true" already indicates "has_gicv4_1==true".  So this
can be simplified.

But I wonder that should we use nassgireq to *only* keep track what
the guest had written into the GICD_CTLR.nASSGIreq.  If not, we may
lose the guest-request bit after migration among hosts with different
has_gicv4_1 settings.


The remaining patches all look good to me :-). I will wait for you to
confirm these two concerns.


Thanks,
Zenghui

> +			value |= GICD_CTLR_nASSGIreq;
>   		break;
>   	case GICD_TYPER:
>   		value = vgic->nr_spis + VGIC_NR_PRIVATE_IRQS;
> @@ -81,6 +84,10 @@ static unsigned long vgic_mmio_read_v3_misc(struct kvm_vcpu *vcpu,
>   			value |= (INTERRUPT_ID_BITS_SPIS - 1) << 19;
>   		}
>   		break;
> +	case GICD_TYPER2:
> +		if (kvm_vgic_global_state.has_gicv4_1)
> +			value = GICD_TYPER2_nASSGIcap;
> +		break;
>   	case GICD_IIDR:
>   		value = (PRODUCT_ID_KVM << GICD_IIDR_PRODUCT_ID_SHIFT) |
>   			(vgic->implementation_rev << GICD_IIDR_REVISION_SHIFT) |
> @@ -98,17 +105,43 @@ static void vgic_mmio_write_v3_misc(struct kvm_vcpu *vcpu,
>   				    unsigned long val)
>   {
>   	struct vgic_dist *dist = &vcpu->kvm->arch.vgic;
> -	bool was_enabled = dist->enabled;
>   
>   	switch (addr & 0x0c) {
> -	case GICD_CTLR:
> +	case GICD_CTLR: {
> +		bool was_enabled, is_hwsgi;
> +
> +		mutex_lock(&vcpu->kvm->lock);
> +
> +		was_enabled = dist->enabled;
> +		is_hwsgi = dist->nassgireq;
> +
>   		dist->enabled = val & GICD_CTLR_ENABLE_SS_G1;
>   
> +		/* Not a GICv4.1? No HW SGIs */
> +		if (!kvm_vgic_global_state.has_gicv4_1)
> +			val &= ~GICD_CTLR_nASSGIreq;
> +
> +		/* Dist stays enabled? nASSGIreq is RO */
> +		if (was_enabled && dist->enabled) {
> +			val &= ~GICD_CTLR_nASSGIreq;
> +			val |= FIELD_PREP(GICD_CTLR_nASSGIreq, is_hwsgi);
> +		}
> +
> +		/* Switching HW SGIs? */
> +		dist->nassgireq = val & GICD_CTLR_nASSGIreq;
> +		if (is_hwsgi != dist->nassgireq)
> +			vgic_v4_configure_vsgis(vcpu->kvm);
> +
>   		if (!was_enabled && dist->enabled)
>   			vgic_kick_vcpus(vcpu->kvm);
> +
> +		mutex_unlock(&vcpu->kvm->lock);
>   		break;
> +	}
>   	case GICD_TYPER:
> +	case GICD_TYPER2:
>   	case GICD_IIDR:
> +		/* This is at best for documentation purposes... */
>   		return;
>   	}
>   }
> @@ -117,10 +150,21 @@ static int vgic_mmio_uaccess_write_v3_misc(struct kvm_vcpu *vcpu,
>   					   gpa_t addr, unsigned int len,
>   					   unsigned long val)
>   {
> +	struct vgic_dist *dist = &vcpu->kvm->arch.vgic;
> +
>   	switch (addr & 0x0c) {
>   	case GICD_IIDR:
>   		if (val != vgic_mmio_read_v3_misc(vcpu, addr, len))
>   			return -EINVAL;
> +		return 0;
> +	case GICD_CTLR:
> +		/* Not a GICv4.1? No HW SGIs */
> +		if (!kvm_vgic_global_state.has_gicv4_1)
> +			val &= ~GICD_CTLR_nASSGIreq;
> +
> +		dist->enabled = val & GICD_CTLR_ENABLE_SS_G1;
> +		dist->nassgireq = val & GICD_CTLR_nASSGIreq;
> +		return 0;
>   	}
>   
>   	vgic_mmio_write_v3_misc(vcpu, addr, len, val);
> diff --git a/virt/kvm/arm/vgic/vgic-v3.c b/virt/kvm/arm/vgic/vgic-v3.c
> index 1bc09b523486..2c9fc13e2c59 100644
> --- a/virt/kvm/arm/vgic/vgic-v3.c
> +++ b/virt/kvm/arm/vgic/vgic-v3.c
> @@ -540,6 +540,8 @@ int vgic_v3_map_resources(struct kvm *kvm)
>   		goto out;
>   	}
>   
> +	if (kvm_vgic_global_state.has_gicv4_1)
> +		vgic_v4_configure_vsgis(kvm);
>   	dist->ready = true;
>   
>   out: