Re: [PATCH v2 3/5] iommu/vt-d: Extend dmar_domain to support nested domain

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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@xxxxxxxxxxxxxxx>

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@xxxxxxxxxxxxxxx>
Signed-off-by: Yi Liu <yi.l.liu@xxxxxxxxx>
---
  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



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