linux-kernel - Re: [RFC PATCH 6/6] iommu/amd: Introduce nested translation support

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Message-ID: <d2cc19fc-f8c6-4b3a-ba88-5db947fb1604@amd.com>
Date: Fri, 5 Jan 2024 20:39:52 +0700
From: "Suthikulpanit, Suravee" <suravee.suthikulpanit@....com>
To: "Tian, Kevin" <kevin.tian@...el.com>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 "iommu@...ts.linux.dev" <iommu@...ts.linux.dev>,
 "joro@...tes.org" <joro@...tes.org>, "jgg@...dia.com" <jgg@...dia.com>
Cc: "Liu, Yi L" <yi.l.liu@...el.com>,
 "nicolinc@...dia.com" <nicolinc@...dia.com>,
 "eric.auger@...hat.com" <eric.auger@...hat.com>,
 "vasant.hegde@....com" <vasant.hegde@....com>,
 "jon.grimm@....com" <jon.grimm@....com>,
 "santosh.shukla@....com" <santosh.shukla@....com>,
 "Dhaval.Giani@....com" <Dhaval.Giani@....com>,
 "pandoh@...gle.com" <pandoh@...gle.com>,
 "loganodell@...gle.com" <loganodell@...gle.com>
Subject: Re: [RFC PATCH 6/6] iommu/amd: Introduce nested translation support

Hi Kevin,

On 12/15/2023 2:45 PM, Tian, Kevin wrote:
>> From: Suravee Suthikulpanit <suravee.suthikulpanit@....com>
>> Sent: Wednesday, December 13, 2023 12:02 AM
>>
>> To support nested translation on AMD IOMMU, the driver needs to
>> program DTE[GCR3 Table Root Pointer] with the address provided by
>> the guest via struct iommu_hwpt_amd_v2, which is passed as a parameter
>> of the struct iommu_ops.domain_alloc_user() with the flag
>> IOMMU_HWPT_ALLOC_NEST_PARENT.
>>
>> Note that current implementation only support GCR3TRPMode for
>> nested translation, which uses GPA to program GCR3 Table Root Pointer.
>>
> 
> means there is a plan to support another mode in the future or
> actually the nested translation requires GCR3TRPMode as a
> functional requirement? imho the point of GPA is assumed
> in the nested configuration in concept...

On (older) system, which does not support GCR3TRPMode, the IOMMU driver 
needs to program the device's DTE[GCR3 Table Root Pointer] field w/ SPA.

When QEMU presents an AMD vIOMMU device to a guest, the guest programs 
the guest DTE[GCR3 Table Root Pointer] with GPA. Then we need to :
1. Traps the DTE write
2. Translate the GPA->SPA
3. Program DTE with SPA.

With the GCR3TRPMode, we can skip step 2 above and directly program step 
3 with GPA.

Suravee