linux-kernel - RE: [PATCH v3 4/6] iommu/vt-d: Setup pasid entries for iova over first level

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Date:   Tue, 17 Dec 2019 02:33:30 +0000
From:   "Liu, Yi L" <yi.l.liu@...el.com>
To:     Lu Baolu <baolu.lu@...ux.intel.com>,
        Joerg Roedel <joro@...tes.org>,
        "David Woodhouse" <dwmw2@...radead.org>,
        Alex Williamson <alex.williamson@...hat.com>
CC:     "Raj, Ashok" <ashok.raj@...el.com>,
        "Kumar, Sanjay K" <sanjay.k.kumar@...el.com>,
        "jacob.jun.pan@...ux.intel.com" <jacob.jun.pan@...ux.intel.com>,
        "Tian, Kevin" <kevin.tian@...el.com>,
        "Sun, Yi Y" <yi.y.sun@...el.com>, Peter Xu <peterx@...hat.com>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "kvm@...r.kernel.org" <kvm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH v3 4/6] iommu/vt-d: Setup pasid entries for iova over
 first level

> From: Lu Baolu < baolu.lu@...ux.intel.com >
> Sent: Tuesday, December 17, 2019 10:04 AM
> To: Liu, Yi L <yi.l.liu@...el.com>; Joerg Roedel <joro@...tes.org>; David
> Woodhouse <dwmw2@...radead.org>; Alex Williamson
> <alex.williamson@...hat.com>
> Subject: Re: [PATCH v3 4/6] iommu/vt-d: Setup pasid entries for iova over first level
> 
> Hi Yi,
> 
> On 12/15/19 5:37 PM, Liu, Yi L wrote:
> >> XD (bit 63) is only for the first level, and SNP (bit 11) is only for
> >> second level, right? I think we need to always set XD bit for IOVA over FL case.
> thoughts?
> > Oops, I made a mistake here. Please forget SNP bit, there is no way to
> > control SNP with first level page table.:-)
> >
> > Actually, it is execute (bit 1) of second level page table which I wanted to say.
> > If software sets R/W/X permission to an IOVA, with IOVA over second
> > level page table, it will set bit 1. However, if IOVA is over first
> > level page table, it may need to clear XD bit. This is what I want to
> > say here. If IOVA doesn’t allow execute permission, it's ok to always
> > set XD bit for IOVA over FL case. But I would like to do it just as
> > what we did for R/W permission. R/W permission relies on the permission
> configured by the page map caller. right?
> 
> Got your point.
> 
> Current driver always cleard X (bit 2) in the second level page table.
> So we will always set XD bit (bit 63) in the first level page table.

yes, I also noticed X (bit 2) is not used in intel-iommu driver. So I
know why you set XD for IOVA over FL case. But it's a little bit weird
to hard code it. That's why I suggested to relay page map caller's
permission input.

> If we decide to use the X permission, we need a separated patch, right?

sure, it would be a separate patch since current code doesn’t apply
X permission.

Regards,
Yi Liu