linux-kernel - Re: [PATCH v2 5/8] iommu/vt-d: Add first level page table interfaces

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Date:   Tue, 3 Dec 2019 10:36:48 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Jacob Pan <jacob.jun.pan@...ux.intel.com>
Cc:     baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        ashok.raj@...el.com, sanjay.k.kumar@...el.com,
        kevin.tian@...el.com, yi.l.liu@...el.com, yi.y.sun@...el.com,
        Peter Xu <peterx@...hat.com>, iommu@...ts.linux-foundation.org,
        kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Yi Sun <yi.y.sun@...ux.intel.com>
Subject: Re: [PATCH v2 5/8] iommu/vt-d: Add first level page table interfaces

Hi,

On 12/3/19 7:27 AM, Jacob Pan wrote:
> On Thu, 28 Nov 2019 10:25:47 +0800
> Lu Baolu<baolu.lu@...ux.intel.com>  wrote:
> 
>> This adds functions to manipulate first level page tables
>> which could be used by a scalale mode capable IOMMU unit.
>>
> FL and SL page tables are very similar, and I presume we are not using
> all the flag bits in FL paging structures for DMA mapping. Are there
> enough relevant differences to warrant a new set of helper functions
> for FL? Or we can merge into one.
> 

I ever thought about this and I am still open for this suggestion.

We had a quick compare on these two page tables. The only concern is the
read/write/present encoding. The present bit in first level implies read
permission while second level page table explicitly has a READ bit.
(recalled from memory, correct me if it's bad. :-)).

Anyway, let's listen to more opinions.

Best regards,
baolu