linux-kernel - Re: [RFC PATCH 0/4] Use 1st-level for DMA remapping in guest

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Message-ID: <dfd9b7a2-5553-328a-08eb-16c8a3a2644e@linux.intel.com>
Date:   Wed, 25 Sep 2019 10:48:32 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     "Tian, Kevin" <kevin.tian@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        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>,
        "Kumar, Sanjay K" <sanjay.k.kumar@...el.com>,
        "Liu, Yi L" <yi.l.liu@...el.com>, "Sun, Yi Y" <yi.y.sun@...el.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: [RFC PATCH 0/4] Use 1st-level for DMA remapping in guest

Hi Kevin,

On 9/24/19 3:00 PM, Tian, Kevin wrote:
>>>>       '-----------'
>>>>       '-----------'
>>>>
>>>> This patch series only aims to achieve the first goal, a.k.a using
> first goal? then what are other goals? I didn't spot such information.
> 

The overall goal is to use IOMMU nested mode to avoid shadow page table
and VMEXIT when map an gIOVA. This includes below 4 steps (maybe not
accurate, but you could get the point.)

1) GIOVA mappings over 1st-level page table;
2) binding vIOMMU 1st level page table to the pIOMMU;
3) using pIOMMU second level for GPA->HPA translation;
4) enable nested (a.k.a. dual stage) translation in host.

This patch set aims to achieve 1).

> Also earlier you mentioned the new approach (nested) is more secure
> than shadowing. why?
> 

My bad! After reconsideration, I realized that it's not "more secure".

Thanks for pointing this out.

Best regards,
Baolu