linux-kernel - Re: [PATCH v2 3/5] iommu/vt-d: Extend dmar

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Message-ID: <0a91496c-d70a-6a52-ab9d-7e3615250d99@linux.intel.com>
Date:   Tue, 21 Mar 2023 09:58:24 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Jason Gunthorpe <jgg@...dia.com>, Yi Liu <yi.l.liu@...el.com>
Cc:     baolu.lu@...ux.intel.com, joro@...tes.org,
        alex.williamson@...hat.com, kevin.tian@...el.com,
        robin.murphy@....com, cohuck@...hat.com, eric.auger@...hat.com,
        nicolinc@...dia.com, kvm@...r.kernel.org, mjrosato@...ux.ibm.com,
        chao.p.peng@...ux.intel.com, yi.y.sun@...ux.intel.com,
        peterx@...hat.com, jasowang@...hat.com,
        shameerali.kolothum.thodi@...wei.com, lulu@...hat.com,
        suravee.suthikulpanit@....com, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org, linux-kselftest@...r.kernel.org
Subject: Re: [PATCH v2 3/5] iommu/vt-d: Extend dmar_domain to support nested
 domain

On 3/20/23 9:54 PM, Jason Gunthorpe wrote:
> On Thu, Mar 09, 2023 at 12:22:05AM -0800, Yi Liu wrote:
>> From: Lu Baolu <baolu.lu@...ux.intel.com>
>>
>> The nested domain fields are exclusive to those that used for a DMA
>> remapping domain. Use union to avoid memory waste.
>>
>> Signed-off-by: Lu Baolu <baolu.lu@...ux.intel.com>
>> Signed-off-by: Yi Liu <yi.l.liu@...el.com>
>> ---
>>   drivers/iommu/intel/iommu.h | 35 +++++++++++++++++++++++++++++------
>>   1 file changed, 29 insertions(+), 6 deletions(-)
> 
> Using unions like this often devolves into a mess.
> 
> You'd be better to have more structures
> 
> struct intel_iommu_domain {
>     struct iommu_domain domain;
>     [general fields about attachment]
> };
> 
> struct intel_iopte_domain {
>      struct intel_iommu_domain domain;
>      [stuff describing the io page table data, pgd, format, etc]
> };
> 
> strut intel_s1_domain {
>       struct intel_iommu_domain domain;
>       struct dmar_domain *s2_domain;
>       /* user page table pointer (in GPA) */
>       unsigned long s1_pgtbl;
>       /* page table attributes */
>       struct iommu_hwpt_intel_vtd s1_cfg;
> };
> static_assert(offset_of(struct intel_s1_domain, domain.domain) ==
>                offset_of(struct intel_iommu_domain, domain));
> 
> The per-domain ops allow to make this work sensibly

Yes. This will make the data structures clearer.

However, this will lead to significant code changes. I think it would be
more appropriate to put it in a separate refactoring series later.

Best regards,
baolu