Hey,
I’ve been investigating the relationship between iommu groups and domains
on our systems and have a few question. Why does the intel iommu code not
allow allocating IOMMU_DOMAIN_DMA? Returning NULL when given this domain
type has the side effect that the default_domain for an iommu group is not
set, which, when using for e.g. dma_map_ops.map_page, means a domain is
allocated per device.
This seems to be the opposite behaviour to the AMD iommu code which
supports allocating an IOMMU_DOMAIN_DMA and will only look to the iommu
group if a domain is not attached to the device rather than allocating a
new one. On AMD every device in an iommu group will share the same domain.
Appended is what I think a patch to implement domain_alloc for
IOMMU_DOMAIN_DMA and also IOMMU_DOMAIN_IDENTITY would look like. Testing
shows each device in a group will share a domain by default, it also
allows allocating a new dma domain that can be successfully attached to a
group with iommu_attach_group.
Looking for comment on why the behaviour is how it is currently and if
there are any issues with the solution I’ve been testing.
Cheers,
James.
diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
index bff2abd6..3a58389f 100644
--- a/drivers/iommu/intel-iommu.c
+++ b/drivers/iommu/intel-iommu.c
@@ -5170,10 +5170,15 @@ static struct iommu_domain
*intel_iommu_domain_alloc(unsigned type)
struct dmar_domain *dmar_domain;
struct iommu_domain *domain;
- if (type != IOMMU_DOMAIN_UNMANAGED)
+ if (type == IOMMU_DOMAIN_UNMANAGED)
+ dmar_domain = alloc_domain(DOMAIN_FLAG_VIRTUAL_MACHINE);
+ else if(type == IOMMU_DOMAIN_DMA)
+ dmar_domain = alloc_domain(0);
+ else if(type == IOMMU_DOMAIN_IDENTITY)
+ dmar_domain = alloc_domain(DOMAIN_FLAG_STATIC_IDENTITY);
+ else
return NULL;
- dmar_domain = alloc_domain(DOMAIN_FLAG_VIRTUAL_MACHINE);
if (!dmar_domain) {
pr_err("Can't allocate dmar_domain\n");
return NULL;
@@ -5186,9 +5191,12 @@ static struct iommu_domain
*intel_iommu_domain_alloc(unsigned type)
domain_update_iommu_cap(dmar_domain);
domain = &dmar_domain->domain;
- domain->geometry.aperture_start = 0;
- domain->geometry.aperture_end = __DOMAIN_MAX_ADDR(dmar_domain->gaw);
- domain->geometry.force_aperture = true;
+
+ if (type == IOMMU_DOMAIN_UNMANAGED) {
+ domain->geometry.aperture_start = 0;
+ domain->geometry.aperture_end =
__DOMAIN_MAX_ADDR(dmar_domain->gaw);
+ domain->geometry.force_aperture = true;
+ }
return domain;
}
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