On 22/09/2023 23.21, Robin Murphy wrote:
On 22/09/2023 2:40 pm, Hector Martin wrote:
Commit a4fdd9762272 ("iommu: Use flush queue capability") hid the IOMMU_DOMAIN_DMA_FQ domain type from domain allocation. A check was introduced in iommu_dma_init_domain() to fall back if not supported, but this check runs too late: by that point, devices have been attached to the IOMMU, and the IOMMU driver might not expect FQ domains at ops->attach_dev() time.
Ensure that we immediately clamp FQ domains to plain DMA if not supported by the driver at device attach time, not later.
This regressed apple-dart in v6.5.
Apologies, I missed that apple-dart was doing something unusual here. However, could we just fix that directly instead?
diff --git a/drivers/iommu/apple-dart.c b/drivers/iommu/apple-dart.c index 2082081402d3..0b8927508427 100644 --- a/drivers/iommu/apple-dart.c +++ b/drivers/iommu/apple-dart.c @@ -671,8 +671,7 @@ static int apple_dart_attach_dev(struct iommu_domain *domain, return ret;
switch (domain->type) {
- case IOMMU_DOMAIN_DMA:
- case IOMMU_DOMAIN_UNMANAGED:
- default: ret = apple_dart_domain_add_streams(dart_domain, cfg); if (ret) return ret;
That's pretty much where we're headed with the domain_alloc_paging redesign anyway - at the driver level, operations on a paging domain should not need to know about the higher-level usage intent of that domain. Ideally, blocking and identity domains should have their own distinct ops now as well, but that might be a bit too big a change for an immediate fix here.
Sure, but it sounded like if there's a capability for this the core should probably use it and not expose the type at all to drivers that can't support it :)
If you think defaulting to that branch in DART is correctly future-proof I can make that change. It's not the only driver checking the domain type in attach_dev(), but it might be the only one enumerating all the options instead of checking for specific cases only (e.g. intel checks for IOMMU_DOMAIN_IDENTITY).
- Hector