linux-kernel - Re: [PATCH 4/5] iommu/vt-d: Add support for static identity domain

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Date:   Thu, 30 Nov 2023 14:09:52 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...dia.com>
Cc:     baolu.lu@...ux.intel.com, Joerg Roedel <joro@...tes.org>,
        Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Kevin Tian <kevin.tian@...el.com>, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/5] iommu/vt-d: Add support for static identity domain

On 2023/11/30 4:28, Jason Gunthorpe wrote:
> On Wed, Nov 29, 2023 at 04:26:15PM -0400, Jason Gunthorpe wrote:
>> On Mon, Nov 20, 2023 at 07:29:43PM +0800, Lu Baolu wrote:
>>
>>> @@ -2311,6 +2316,13 @@ static int device_def_domain_type(struct device *dev)
>>>   			return IOMMU_DOMAIN_IDENTITY;
>>>   	}
>>>   
>>> +	/*
>>> +	 * Hardware does not support the passthrough translation mode.
>>> +	 * Always use a dynamaic mapping domain.
>>> +	 */
>>> +	if (!ecap_pass_through(iommu->ecap))
>>> +		return IOMMU_DOMAIN_DMA;
>>> +
>> Doesn't this return from def_domain_type completely prevent using an
>> identity domain?
>>
>> I thought the point of this was to allow the identity domain but have
>> it be translating?
> I suppose the answer is the next patch deletes that stuff.
> 
> I would probably have structured this in the other order, first add
> this hunk and say that old HW is being de-supported. Remove all the
> now-dead code creating the 1:1 page table, then refactor the remainder
> to create the global static.

Okay, that would be more readable.

Best regards,
baolu