Re: [RFC PATCH v3 1/2] iommu: Add capability IOMMU_CAP_VIOMMU

[Jason Wang <jasowang@xxxxxxxxxx>]

On 2021/1/14 上午9:30, Lu Baolu wrote:
> Some vendor IOMMU drivers are able to declare that it is running in a VM
> context. This is very valuable for the features that only want to be
> supported on bare metal. Add a capability bit so that it could be used.
>
> Signed-off-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>
> ---
>   drivers/iommu/intel/iommu.c  | 20 ++++++++++++++++++++
>   drivers/iommu/virtio-iommu.c |  9 +++++++++
>   include/linux/iommu.h        |  1 +
>   3 files changed, 30 insertions(+)
>
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index cb205a04fe4c..8eb022d0e8aa 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -5738,12 +5738,32 @@ static inline bool nested_mode_support(void)
>   	return ret;
>   }
>   
> +static inline bool caching_mode_enabled(void)
> +{
> +	struct dmar_drhd_unit *drhd;
> +	struct intel_iommu *iommu;
> +	bool ret = false;
> +
> +	rcu_read_lock();
> +	for_each_active_iommu(iommu, drhd) {
> +		if (cap_caching_mode(iommu->cap)) {
> +			ret = true;
> +			break;
> +		}
> +	}
> +	rcu_read_unlock();
> +
> +	return ret;
> +}
> +
>   static bool intel_iommu_capable(enum iommu_cap cap)
>   {
>   	if (cap == IOMMU_CAP_CACHE_COHERENCY)
>   		return domain_update_iommu_snooping(NULL) == 1;
>   	if (cap == IOMMU_CAP_INTR_REMAP)
>   		return irq_remapping_enabled == 1;
> +	if (cap == IOMMU_CAP_VIOMMU)
> +		return caching_mode_enabled();


This part I don't understand. Does it mean Intel IOMMU can't be used in 
VM without caching mode?

Thanks


>   
>   	return false;
>   }
> diff --git a/drivers/iommu/virtio-iommu.c b/drivers/iommu/virtio-iommu.c
> index 2bfdd5734844..719793e103db 100644
> --- a/drivers/iommu/virtio-iommu.c
> +++ b/drivers/iommu/virtio-iommu.c
> @@ -931,7 +931,16 @@ static int viommu_of_xlate(struct device *dev, struct of_phandle_args *args)
>   	return iommu_fwspec_add_ids(dev, args->args, 1);
>   }
>   
> +static bool viommu_capable(enum iommu_cap cap)
> +{
> +	if (cap == IOMMU_CAP_VIOMMU)
> +		return true;
> +
> +	return false;
> +}
> +
>   static struct iommu_ops viommu_ops = {
> +	.capable		= viommu_capable,
>   	.domain_alloc		= viommu_domain_alloc,
>   	.domain_free		= viommu_domain_free,
>   	.attach_dev		= viommu_attach_dev,
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index b95a6f8db6ff..1d24be667a03 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -94,6 +94,7 @@ enum iommu_cap {
>   					   transactions */
>   	IOMMU_CAP_INTR_REMAP,		/* IOMMU supports interrupt isolation */
>   	IOMMU_CAP_NOEXEC,		/* IOMMU_NOEXEC flag */
> +	IOMMU_CAP_VIOMMU,		/* IOMMU can declar running in a VM */
>   };
>   
>   /*