linux-kernel - Re: [PATCH v4 15/16] iommu/amd: Refactor logic to program the host page table in DTE

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Message-ID: <8c534f45-80ee-4537-93b5-2643afccde8c@amd.com>
Date: Thu, 13 Nov 2025 01:40:47 +0700
From: "Suthikulpanit, Suravee" <suravee.suthikulpanit@....com>
To: Jason Gunthorpe <jgg@...dia.com>, Vasant Hegde <vasant.hegde@....com>
Cc: nicolinc@...dia.com, linux-kernel@...r.kernel.org, robin.murphy@....com,
 will@...nel.org, joro@...tes.org, kevin.tian@...el.com, jsnitsel@...hat.com,
 iommu@...ts.linux.dev, santosh.shukla@....com, sairaj.arunkodilkar@....com,
 jon.grimm@....com, prashanthpra@...gle.com, wvw@...gle.com,
 wnliu@...gle.com, gptran@...gle.com, kpsingh@...gle.com,
 joao.m.martins@...cle.com, alejandro.j.jimenez@...cle.com
Subject: Re: [PATCH v4 15/16] iommu/amd: Refactor logic to program the host
 page table in DTE



On 11/9/2025 6:03 AM, Jason Gunthorpe wrote:
> On Sat, Nov 08, 2025 at 10:56:38PM +0530, Vasant Hegde wrote:
>> On 10/23/2025 6:38 PM, Jason Gunthorpe wrote: 
>>> On Tue, Oct 21, 2025 at 01:43:23AM +0000, Suravee Suthikulpanit wrote:
>>>
>>> (though how does IDENTITY on a device with a PASID installed work?)
>>
>> Probably set_dte_identity() should call  set_dte_gcr3_table () and update
>> relevant fields.

Actually, PASID would not work with IDENTITY since it has no page table 
(i.e. iommu=pt means DTE[Mode]=0 and does not have host table pointer).
PASID only work with GCR3 table.

Therefore, it does not make sense for set_dte_identity() to call 
set_dte_gcr3_table(). Each one should be stand alone.

Thanks,
Suravee

> Yeah, maybe so, though it might be best if the caller can detect it
> and have it call both functions instead of trying to bury it.
> 
> There is a fair number of variations here as you have
> blocked/identity, RID/PASID attach and PASID detach to all consider.
> 
> It would be nice if it worked properly, identity on RID while PASID is
> in use has a strong real use case.
> 
> Jason