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 10:03:41 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
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>
Cc:     baolu.lu@...ux.intel.com, "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

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

Best regards,
baolu