linux-kernel - Re: [PATCH v2 2/2] iommu/vt-d: Enable PASID only if device expects PASID in PRG Response.

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Date:   Wed, 13 Feb 2019 10:10:46 -0800
From:   "Raj, Ashok" <ashok.raj@...el.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>
Cc:     "sathyanarayanan.kuppuswamy@...ux.intel.com" 
        <sathyanarayanan.kuppuswamy@...ux.intel.com>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "dwmw2@...radead.org" <dwmw2@...radead.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Busch, Keith" <keith.busch@...el.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>
Subject: Re: [PATCH v2 2/2] iommu/vt-d: Enable PASID only if device expects
 PASID  in PRG Response.

On Wed, Feb 13, 2019 at 12:26:33AM -0800, Tian, Kevin wrote:
> > 
> > diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> > index 1457f931218e..af2e4a011787 100644
> > --- a/drivers/iommu/intel-iommu.c
> > +++ b/drivers/iommu/intel-iommu.c
> > @@ -1399,7 +1399,8 @@ static void iommu_enable_dev_iotlb(struct
> > device_domain_info *info)
> >  	   undefined. So always enable PASID support on devices which
> >  	   have it, even if we can't yet know if we're ever going to
> >  	   use it. */
> > -	if (info->pasid_supported && !pci_enable_pasid(pdev, info-
> > >pasid_supported & ~1))
> > +	if (info->pasid_supported && pci_prg_resp_pasid_required(pdev)
> > &&
> > +	    !pci_enable_pasid(pdev, info->pasid_supported & ~1))
> >  		info->pasid_enabled = 1;
> 
> Above logic looks problematic. As Dave commented in another thread,
> PRI and PASID are orthogonal capabilities. Especially with introduction
> of VT-d scalable mode, PASID will be used alone even w/o PRI...
> 
> Why not doing the check when PRI is actually enabled? At that point
> you can fail the request if above condition is false. 
> 

That makes sense.