linux-kernel - Re: [PATCH v6 01/10] iommu/vt-d: Enlightened PASID allocation

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Date:   Wed, 23 Oct 2019 14:11:26 -0700
From:   Jacob Pan <jacob.jun.pan@...ux.intel.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>
Cc:     "Raj, Ashok" <ashok.raj@...el.com>,
        iommu@...ts.linux-foundation.org,
        LKML <linux-kernel@...r.kernel.org>,
        Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        Jean-Philippe Brucker <jean-philippe@...aro.com>,
        Yi Liu <yi.l.liu@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        Christoph Hellwig <hch@...radead.org>,
        Jonathan Cameron <jic23@...nel.org>,
        Eric Auger <eric.auger@...hat.com>,
        jacob.jun.pan@...ux.intel.com
Subject: Re: [PATCH v6 01/10] iommu/vt-d: Enlightened PASID allocation

On Wed, 23 Oct 2019 10:55:23 -0700
Jacob Pan <jacob.jun.pan@...ux.intel.com> wrote:

> > > Do you have to check this everytime? every dmar_readq is going to
> > > trap to the other side ...    
> > 
> > Yes. We don't need to check it every time. Check once and save the
> > result during boot is enough.
> > 
> > How about below incremental change?
> >   
> Below is good but I was thinking to include vccap in struct
> intel_iommu{} where cap and ecaps reside. i.e.
> diff --git a/include/linux/intel-iommu.h b/include/linux/intel-iommu.h
> index 14b87ae2916a..e2cf25c9c956 100644
> --- a/include/linux/intel-iommu.h
> +++ b/include/linux/intel-iommu.h
> @@ -528,6 +528,7 @@ struct intel_iommu {
>         u64             reg_size; /* size of hw register set */
>         u64             cap;
>         u64             ecap;
> +       u64             vccap;
> 
> Also, we can use a static branch here.
> 
On a second thought, we cannot use static(branch) here in that we
cannot assume there is only one vIOMMU all the time. Have to cache the
vccap per iommu.

> > diff --git a/drivers/iommu/intel-pasid.c
> > b/drivers/iommu/intel-pasid.c index ff7e877b7a4d..c15d9d7e1e73
> > 100644 --- a/drivers/iommu/intel-pasid.c
> > +++ b/drivers/iommu/intel-pasid.c
> > @@ -29,22 +29,29 @@ u32 intel_pasid_max_id = PASID_MAX;
> > 
[Jacob Pan]