Re: [PATCH v3 1/4] KVM: arm64: GICv4.1: Add function to get VLPI state

[Shenming Lu]

On 2021/3/11 16:57, Marc Zyngier wrote:
> On Wed, 27 Jan 2021 12:13:34 +0000,
> Shenming Lu <lushenming@xxxxxxxxxx> wrote:
>>
>> With GICv4.1 and the vPE unmapped, which indicates the invalidation
>> of any VPT caches associated with the vPE, we can get the VLPI state
>> by peeking at the VPT. So we add a function for this.
>>
>> Signed-off-by: Shenming Lu <lushenming@xxxxxxxxxx>
>> ---
>>  arch/arm64/kvm/vgic/vgic-v4.c | 19 +++++++++++++++++++
>>  arch/arm64/kvm/vgic/vgic.h    |  1 +
>>  2 files changed, 20 insertions(+)
>>
>> diff --git a/arch/arm64/kvm/vgic/vgic-v4.c b/arch/arm64/kvm/vgic/vgic-v4.c
>> index 66508b03094f..ac029ba3d337 100644
>> --- a/arch/arm64/kvm/vgic/vgic-v4.c
>> +++ b/arch/arm64/kvm/vgic/vgic-v4.c
>> @@ -203,6 +203,25 @@ void vgic_v4_configure_vsgis(struct kvm *kvm)
>>  	kvm_arm_resume_guest(kvm);
>>  }
>>  
>> +/*
>> + * Must be called with GICv4.1 and the vPE unmapped, which
>> + * indicates the invalidation of any VPT caches associated
>> + * with the vPE, thus we can get the VLPI state by peeking
>> + * at the VPT.
>> + */
>> +void vgic_v4_get_vlpi_state(struct vgic_irq *irq, bool *val)
>> +{
>> +	struct its_vpe *vpe = &irq->target_vcpu->arch.vgic_cpu.vgic_v3.its_vpe;
>> +	int mask = BIT(irq->intid % BITS_PER_BYTE);
>> +	void *va;
>> +	u8 *ptr;
>> +
>> +	va = page_address(vpe->vpt_page);
>> +	ptr = va + irq->intid / BITS_PER_BYTE;
>> +
>> +	*val = !!(*ptr & mask);
> 
> What guarantees that you can actually read anything valid? Yes, the
> VPT caches are clean. But that doesn't make them coherent with CPU
> caches.
> 
> You need some level of cache maintenance here.

Yeah, and you have come up with some codes for this in v2:

diff --git a/drivers/irqchip/irq-gic-v3-its.c
b/drivers/irqchip/irq-gic-v3-its.c
index 7db602434ac5..2dbef127ca15 100644
--- a/drivers/irqchip/irq-gic-v3-its.c
+++ b/drivers/irqchip/irq-gic-v3-its.c
@@ -4552,6 +4552,10 @@ static void its_vpe_irq_domain_deactivate(struct
irq_domain *domain,

  		its_send_vmapp(its, vpe, false);
  	}
+
+	if (find_4_1_its() && !atomic_read(vpe->vmapp_count))
+		gic_flush_dcache_to_poc(page_address(vpe->vpt_page),
+					LPI_PENDBASE_SZ);
  }

  static const struct irq_domain_ops its_vpe_domain_ops = {

Could I add it to this series? :-)

Thanks,
Shenming

> 
> Thanks,
> 
> 	M.
>