linux-kernel - Re: [PATCH] iommu: Update the document of IOMMU_DOMAIN

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Date:   Tue, 2 Feb 2021 21:14:29 +0800
From:   Keqian Zhu <zhukeqian1@...wei.com>
To:     Robin Murphy <robin.murphy@....com>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <iommu@...ts.linux-foundation.org>
CC:     Marc Zyngier <maz@...nel.org>,
        Alex Williamson <alex.williamson@...hat.com>,
        <jiangkunkun@...wei.com>, Will Deacon <will@...nel.org>,
        <wanghaibin.wang@...wei.com>
Subject: Re: [PATCH] iommu: Update the document of IOMMU_DOMAIN_UNMANAGED



On 2021/2/2 20:58, Robin Murphy wrote:
> On 2021-02-02 08:53, Keqian Zhu wrote:
>> Signed-off-by: Keqian Zhu <zhukeqian1@...wei.com>
>> ---
>>   include/linux/iommu.h | 2 +-
>>   1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
>> index 77e561ed57fd..e8f2efae212b 100644
>> --- a/include/linux/iommu.h
>> +++ b/include/linux/iommu.h
>> @@ -68,7 +68,7 @@ struct iommu_domain_geometry {
>>    *                  devices
>>    *    IOMMU_DOMAIN_IDENTITY    - DMA addresses are system physical addresses
>>    *    IOMMU_DOMAIN_UNMANAGED    - DMA mappings managed by IOMMU-API user, used
>> - *                  for VMs
>> + *                  for VMs or userspace driver frameworks
> 
> Given that "VMs" effectively has to mean VFIO, doesn't it effectively already imply other uses of VFIO anyway? Unmanaged domains are also used in other subsystems/drivers inside the kernel and we're not naming those, so I don't see that it's particularly helpful to specifically call out one more VFIO use-case.
> 
> Perhaps the current wording could be generalised a little more, but we certainly don't want to start trying to maintain an exhaustive list of users here...
Yep, a more generalised description is better. After I have a look at all the use cases...

Thanks,
Keqian

> 
> Robin.
> 
>>    *    IOMMU_DOMAIN_DMA    - Internally used for DMA-API implementations.
>>    *                  This flag allows IOMMU drivers to implement
>>    *                  certain optimizations for these domains
>>
> .
>