Hi,
On 11/8/18 1:55 AM, James Sewart wrote:
Hey,
On 7 Nov 2018, at 02:10, Lu Baolu <baolu...@linux.intel.com> wrote:
Hi,
On 11/6/18 6:40 PM, James Sewart wrote:
Hey Lu,
Would you be able to go into more detail about the issues with
allowing IOMMU_DOMAIN_DMA to be allocated via domain_alloc?
This door is closed because intel iommu driver does everything for
IOMMU_DOMAIN_DMA: allocating a domain and setup the context entries
for the domain.
As far as I can tell, attach_device in the intel driver will handle
cleaning up any old domain context mapping and ensure the new domain is
mapped with calls to dmar_remove_one_dev_info and domain_add_dev_info.
That's only for domains of IOMMU_DOMAIN_UNMANAGED, right?
Why do we want to open this door? Probably we want the generic iommu
layer to handle these things (it's called default domain).
I’d like to allocate a domain and attach it to multiple devices in a
group/multiple groups so that they share address translation, but still
allow drivers for devices in those groups to use the dma_map_ops api.
Just out of curiosity, why do you want to share a single domain across
multiple groups? By default, the groups and DMA domains are normally
1-1 mapped, right?
So we can't just open the door but not cleanup the things right?
A user of domain_alloc and attach_device is responsible for detaching a
domain if it is no longer needed and calling domain_free.
Currently DMA API calls get_valid_domain_for_dev() to retrieve a DMA
domain. If the domain has already been allocated, return directly.
Otherwise, allocate and initialize a new one for the device. Let's call
domains allocated by get_valid_domain_for_dev() as "A".
If we open the door and allow another component to manage the DMA
domains through domain iommu_domain_alloc/free(). Let's call domains
allocated through iommu_domain_alloc() as "B".
So how can we sync between A and B?
Need to go through the code to find out more.
Best regards,
Lu Baolu
Cheers,
James.
I haven't spent time on details. So I cc'ed Jacob for corrections.
Best regards,
Lu Baolu
Cheers,
James.
On Fri, Nov 2, 2018 at 2:43 AM Lu Baolu <baolu...@linux.intel.com> wrote:
Hi,
On 10/30/18 10:18 PM, James Sewart via iommu wrote:
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.
Intel vt-d driver doesn't implement the default domain and allocates
domain only on demanded. There are lots of things to do before we allow
iommu API to allocate domains other than IOMMU_DOMAIN_UNMANAGED.
Best regards,
Lu Baolu
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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