linux-kernel - Re: 答复: 答复: [PATCH v3 2/2] iommu/vt-d:Add support for probing ACPI device in RMRR

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Date:   Thu, 3 Sep 2020 15:22:14 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     FelixCui-oc <FelixCui-oc@...oxin.com>,
        Joerg Roedel <joro@...tes.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        David Woodhouse <dwmw2@...radead.org>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        "kbuild@...ts.01.org" <kbuild@...ts.01.org>
Cc:     baolu.lu@...ux.intel.com, CobeChen-oc <CobeChen-oc@...oxin.com>,
        RaymondPang-oc <RaymondPang-oc@...oxin.com>,
        Tony W Wang-oc <TonyWWang-oc@...oxin.com>,
        Ashok Raj <ashok.raj@...el.com>
Subject: Re: 答复: 答复: [PATCH v3 2/2] iommu/vt-d:Add support for probing ACPI device in RMRR

Hi Felix,

On 9/2/20 11:24 AM, FelixCui-oc wrote:
> hi baolu,
> 
>> So you have a hidden device (invisible to host kernel). But you need to
> 
>>setup some identity mappings for this device, so that the firmware
>>could keep working, right?
> 
>>The platform designs this by putting that range in the RMRR table and
>>expecting the OS kernel to setup identity mappings during boot.
> 
>>Do I understand it right?
> 
> 
> Yes. What you understand is correct.

This appears to be a new usage model of RMRR. I need to discuss this
with the VT-d spec maintainer. Do you mind telling which platform are
you going to run this on? What is the motivation of creating such hidden
device?

Basically, RMRRs were added as work around for certain legacy device and
we have been working hard to fix those legacy devices so that RMRR are
no longer needed.

Best regards,
baolu