linux-kernel - Re: [PATCH v3 14/15] iommu/amd: Refactor logic to program the host page table in DTE

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Message-ID: <41ed7ddc-58d4-4691-b3fc-1da2c7dc41bd@amd.com>
Date: Mon, 20 Oct 2025 20:26:10 -0500
From: "Suthikulpanit, Suravee" <suravee.suthikulpanit@....com>
To: Jason Gunthorpe <jgg@...dia.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,
 vasant.hegde@....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 v3 14/15] iommu/amd: Refactor logic to program the host
 page table in DTE



On 10/10/2025 6:09 PM, Jason Gunthorpe wrote:
> On Thu, Oct 09, 2025 at 11:57:54PM +0000, Suravee Suthikulpanit wrote:
>> ...
>> @@ -2061,36 +2087,14 @@ static void set_dte_entry(struct amd_iommu *iommu,
>>   
>>   	amd_iommu_make_clear_dte(dev_data, &new);
>>   
>> -	if (domain->iop.mode != PAGE_MODE_NONE)
>> -		new.data[0] |= iommu_virt_to_phys(domain->iop.root);
>> -
>> -	new.data[0] |= (domain->iop.mode & DEV_ENTRY_MODE_MASK)
>> -		    << DEV_ENTRY_MODE_SHIFT;
>> -
>> -	new.data[0] |= DTE_FLAG_IR | DTE_FLAG_IW;
>> +	old_domid = READ_ONCE(dte->data[1]) & DTE_DOMID_MASK;
>>   
>> -	/*
>> -	 * When SNP is enabled, we can only support TV=1 with non-zero domain ID.
>> -	 * This is prevented by the SNP-enable and IOMMU_DOMAIN_IDENTITY check in
>> -	 * do_iommu_domain_alloc().
>> -	 */
>> -	WARN_ON(amd_iommu_snp_en && (domid == 0));
>> -	new.data[0] |= DTE_FLAG_TV;
>> +	set_dte_v1(dev_data, domain, domid, &new);
>> +	set_dte_gcr3_table(iommu, dev_data, &new);
> 
> This seems weird, I would expect this to be written:
> 
> if (gcr3_info && gcr3_info->gcr3_tbl)
> 	set_dte_gcr3_table(iommu, dev_data, &new);
> else
> 	set_dte_v1(dev_data, domain, domid, &new);
> 
> It is nonsense to call both gcr3 and v1 in this function that does not
> setup two stages.
> 
> So, I'd just put this code in both the v1 and gcr3 functions:
> 
>   +	new->data[0] |= DTE_FLAG_IR | DTE_FLAG_IW | DTE_FLAG_TV;
>   +	if (dev_data->ats_enabled)
>   +		new->data[1] |= DTE_FLAG_IOTLB;
> 
> (does IR/IW apply to GCR3?)

IR/IW apply to both host and GCR3 tables. I'll add comment to the V4.

> And then WARN_ON(domain->iop.mode != PAGE_MODE_NONE) as it should be
> illegal to call set_dte_v1() on a domain that is not a v1 domain.

I'll rework the logic in the set_dte_entry() as you suggested in V4.

Thanks,
Suravee

> But this is overall the right idea and direction.
> 
> Jason