linux-kernel - Re: [RFC PATCH v2 02/10] iommu/vt-d: Add multiple domains per device query

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Date:   Wed, 5 Sep 2018 13:35:40 -0600
From:   Alex Williamson <alex.williamson@...hat.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Kirti Wankhede <kwankhede@...dia.com>, ashok.raj@...el.com,
        sanjay.k.kumar@...el.com, jacob.jun.pan@...el.com,
        kevin.tian@...el.com,
        Jean-Philippe Brucker <jean-philippe.brucker@....com>,
        yi.l.liu@...el.com, yi.y.sun@...el.com, peterx@...hat.com,
        tiwei.bie@...el.com, iommu@...ts.linux-foundation.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>
Subject: Re: [RFC PATCH v2 02/10] iommu/vt-d: Add multiple domains per
 device query

On Thu, 30 Aug 2018 12:09:14 +0800
Lu Baolu <baolu.lu@...ux.intel.com> wrote:

> Add the response to IOMMU_CAP_AUX_DOMAIN capability query
> through iommu_capable(). Return true if IOMMUs support the
> scalable mode, return false otherwise.
> 
> Cc: Ashok Raj <ashok.raj@...el.com>
> Cc: Jacob Pan <jacob.jun.pan@...ux.intel.com>
> Cc: Kevin Tian <kevin.tian@...el.com>
> Cc: Liu Yi L <yi.l.liu@...el.com>
> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
> ---
>  drivers/iommu/intel-iommu.c | 31 +++++++++++++++++++++++++++++--
>  1 file changed, 29 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> index 3e49d4029058..891ae70e7bf2 100644
> --- a/drivers/iommu/intel-iommu.c
> +++ b/drivers/iommu/intel-iommu.c
> @@ -5193,12 +5193,39 @@ static phys_addr_t intel_iommu_iova_to_phys(struct iommu_domain *domain,
>  	return phys;
>  }
>  
> +static inline bool scalable_mode_support(void)
> +{
> +	struct dmar_drhd_unit *drhd;
> +	struct intel_iommu *iommu;
> +	bool ret = true;
> +
> +	rcu_read_lock();
> +	for_each_active_iommu(iommu, drhd) {
> +		if (!sm_supported(iommu)) {
> +			ret = false;
> +			break;
> +		}
> +	}
> +	rcu_read_unlock();
> +
> +	return ret;
> +}
> +
>  static bool intel_iommu_capable(enum iommu_cap cap)
>  {
> -	if (cap == IOMMU_CAP_CACHE_COHERENCY)
> +	switch (cap) {
> +	case IOMMU_CAP_CACHE_COHERENCY:
>  		return domain_update_iommu_snooping(NULL) == 1;
> -	if (cap == IOMMU_CAP_INTR_REMAP)
> +	case IOMMU_CAP_INTR_REMAP:
>  		return irq_remapping_enabled == 1;
> +	case IOMMU_CAP_AUX_DOMAIN:
> +		return scalable_mode_support();
> +	case IOMMU_CAP_NOEXEC:
> +	/* PASSTHROUGH */
> +	default:
> +		pr_info("Unsupported capability query %d\n", cap);
> +		break;

Please don't do this, there's no reason to be noisy about a query of a
capability that VT-d doesn't know about.  We implement capabilities
exactly so that relevant drivers can expose a feature and others can
happily (and quietly) ignore them.  Thanks,

Alex