Re: [PATCH v2 8/9] KVM: arm/arm64: vgic-its: Check the LPI translation cache on MSI injection

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Hi Marc,

On 7/23/19 5:45 PM, Marc Zyngier wrote:
> Hi Eric,
> 
> On 23/07/2019 16:10, Auger Eric wrote:
>> Hi Marc,
>>
>> On 6/11/19 7:03 PM, Marc Zyngier wrote:
>>> When performing an MSI injection, let's first check if the translation
>>> is already in the cache. If so, let's inject it quickly without
>>> going through the whole translation process.
>>>
>>> Signed-off-by: Marc Zyngier <marc.zyngier@xxxxxxx>
>>> ---
>>>  virt/kvm/arm/vgic/vgic-its.c | 36 ++++++++++++++++++++++++++++++++++++
>>>  virt/kvm/arm/vgic/vgic.h     |  1 +
>>>  2 files changed, 37 insertions(+)
>>>
>>> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
>>> index 62932458476a..83d80ec33473 100644
>>> --- a/virt/kvm/arm/vgic/vgic-its.c
>>> +++ b/virt/kvm/arm/vgic/vgic-its.c
>>> @@ -577,6 +577,20 @@ static struct vgic_irq *__vgic_its_check_cache(struct vgic_dist *dist,
>>>  	return irq;
>>>  }
>>>  
>>> +static struct vgic_irq *vgic_its_check_cache(struct kvm *kvm, phys_addr_t db,
>>> +					     u32 devid, u32 eventid)
>>> +{
>>> +	struct vgic_dist *dist = &kvm->arch.vgic;
>>> +	struct vgic_irq *irq;
>>> +	unsigned long flags;
>>> +
>>> +	raw_spin_lock_irqsave(&dist->lpi_list_lock, flags);
>>> +	irq = __vgic_its_check_cache(dist, db, devid, eventid);
>>> +	raw_spin_unlock_irqrestore(&dist->lpi_list_lock, flags);
>>> +
>>> +	return irq;
>>> +}
>>> +
>>>  static void vgic_its_cache_translation(struct kvm *kvm, struct vgic_its *its,
>>>  				       u32 devid, u32 eventid,
>>>  				       struct vgic_irq *irq)
>>> @@ -736,6 +750,25 @@ static int vgic_its_trigger_msi(struct kvm *kvm, struct vgic_its *its,
>>>  	return 0;
>>>  }
>>>  
>>> +int vgic_its_inject_cached_translation(struct kvm *kvm, struct kvm_msi *msi)
>>> +{
>>> +	struct vgic_irq *irq;
>>> +	unsigned long flags;
>>> +	phys_addr_t db;
>>> +
>>> +	db = (u64)msi->address_hi << 32 | msi->address_lo;
>>> +	irq = vgic_its_check_cache(kvm, db, msi->devid, msi->data);
>>
>> I think we miss a check of its->enabled. This is currently done in
>> vgic_its_resolve_lpi() but now likely to be bypassed.
> 
> But why would a translation be cached if the ITS is disabled? It should
> never haver been there the first place (vgic_its_resolve_lpi does check
> for the ITS being enabled, as you pointed out).
> 
> Which makes me think that we miss an invalidate on an ITS being disabled:
> 
> diff --git a/virt/kvm/arm/vgic/vgic-its.c b/virt/kvm/arm/vgic/vgic-its.c
> index 2633b0e88981..5f2ad74ad834 100644
> --- a/virt/kvm/arm/vgic/vgic-its.c
> +++ b/virt/kvm/arm/vgic/vgic-its.c
> @@ -1719,6 +1719,8 @@ static void vgic_mmio_write_its_ctlr(struct kvm *kvm, struct vgic_its *its,
>  		goto out;
>  
>  	its->enabled = !!(val & GITS_CTLR_ENABLE);
> +	if (!its->enabled)
> +		vgic_its_invalidate_cache(kvm);
>  
>  	/*
>  	 * Try to process any pending commands. This function bails out early
> 
> 
> What do you think?

Yes I agree this is the right way to fix it.

Thanks

Eric
> 
> 	M.
> 



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