linux-kernel - Re: [PATCH 3/7] iommu/vt-d: Enhance compatibility check for paging domain attach

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Message-ID: <b85a9fb0-f990-4e23-81e3-36546f62d5db@linux.intel.com>
Date: Wed, 16 Oct 2024 09:46:40 +0800
From: Baolu Lu <baolu.lu@...ux.intel.com>
To: Jason Gunthorpe <jgg@...pe.ca>
Cc: baolu.lu@...ux.intel.com, iommu@...ts.linux.dev,
 Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
 Robin Murphy <robin.murphy@....com>, Kevin Tian <kevin.tian@...el.com>,
 Yi Liu <yi.l.liu@...el.com>, Vasant Hegde <vasant.hegde@....com>,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/7] iommu/vt-d: Enhance compatibility check for paging
 domain attach

On 2024/10/15 20:48, Jason Gunthorpe wrote:
> On Tue, Oct 15, 2024 at 10:52:19AM +0800, Baolu Lu wrote:
>> On 2024/10/15 3:24, Jason Gunthorpe wrote:
>>> On Mon, Oct 14, 2024 at 09:25:03AM +0800, Baolu Lu wrote:
>>>>>> +	if (domain->type & __IOMMU_DOMAIN_PAGING) {
>>>>> It looks like this entire function is already never called for
>>>>> anything but paging?
>>>>>
>>>>> The only three callers are:
>>>>>
>>>>> 	.default_domain_ops = &(const struct iommu_domain_ops) {
>>>>> 		.attach_dev		= intel_iommu_attach_device,
>>>>> 		.set_dev_pasid		= intel_iommu_set_dev_pasid,
>>>>>
>>>>> and
>>>>>
>>>>> static const struct iommu_domain_ops intel_nested_domain_ops = {
>>>>> 	.attach_dev		= intel_nested_attach_dev,
>>>>>
>>>>> And none of those cases can be anything except a paging domain by
>>>>> definition.
>>>> A nested domain is not a paging domain. It represents a user-space page
>>>> table that nested on a parent paging domain. Perhaps I overlooked
>>>> anything?
>>> It only calls it on the s2_parent which is always a paging domain?
>>>
>>> 	ret = prepare_domain_attach_device(&dmar_domain->s2_domain->domain, dev);
>> Yea, you are right. I overlooked that part.  I'll remove the 'if'
>> statement and utilize a WARN_ON() function instead.
>>
>> And also, I will rename this function with a meaningful name,some like
>> paging_domain_is_compatible()?
> That sounds good too
> 
> Ultimately you want to try to structure the driver so that there is a
> struct paging_domain that is always the paging domain type and
> everything is easy to understand. Don't re-use the same struct for
> identity/blocked/nested domains.

Yes, agreed!

Thanks,
baolu