linux-kernel - Re: [PATCH 5/6] iommu/vt-d: Cleanup after delegating DMA domain to generic iommu

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Date:   Mon, 10 Jun 2019 12:25:31 -0700
From:   Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>
To:     "Mehta, Sohil" <sohil.mehta@...el.com>,
        "joro@...tes.org" <joro@...tes.org>,
        "baolu.lu@...ux.intel.com" <baolu.lu@...ux.intel.com>,
        "dwmw2@...radead.org" <dwmw2@...radead.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Raj, Ashok" <ashok.raj@...el.com>, "cai@....pw" <cai@....pw>,
        "jacob.jun.pan@...ux.intel.com" <jacob.jun.pan@...ux.intel.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "Pan, Jacob jun" <jacob.jun.pan@...el.com>,
        "Tian, Kevin" <kevin.tian@...el.com>
Subject: Re: [PATCH 5/6] iommu/vt-d: Cleanup after delegating DMA domain to
 generic iommu

On Mon, 2019-06-10 at 11:45 -0700, Mehta, Sohil wrote:
> On Sun, 2019-06-09 at 10:38 +0800, Lu Baolu wrote:
> >  static int __init si_domain_init(int hw)
> > @@ -3306,14 +3252,13 @@ static int __init init_dmars(void)
> >                 if (pasid_supported(iommu))
> >                         intel_svm_init(iommu);
> >  #endif
> > -       }
> >  
> > -       /*
> > -        * Now that qi is enabled on all iommus, set the root entry
> > and flush
> > -        * caches. This is required on some Intel X58 chipsets,
> > otherwise the
> > -        * flush_context function will loop forever and the boot
> > hangs.
> > -        */
> > -       for_each_active_iommu(iommu, drhd) {
> > +               /*
> > +                * Now that qi is enabled on all iommus, set the root
> > entry and
> > +                * flush caches. This is required on some Intel X58
> > chipsets,
> > +                * otherwise the flush_context function will loop
> > forever and
> > +                * the boot hangs.
> > +                */
> >                 iommu_flush_write_buffer(iommu);
> >                 iommu_set_root_entry(iommu);
> >                 iommu->flush.flush_context(iommu, 0, 0, 0,
> > DMA_CCMD_GLOBAL_INVL);
> 
> This changes the intent of the original code. As the comment says
> enable QI on all IOMMUs, then flush the caches and set the root entry.
> The order of setting the root entries has changed now.
> 
> Refer: 
> Commit a4c34ff1c029 ('iommu/vt-d: Enable QI on all IOMMUs before
> setting root entry')

Thanks Sohil! for catching the bug.
Will send a V2 to Lu Baolu fixing this.

Regards,
Sai