[PATCH 17/20] iommu/vt-d: Simplify compatibility check for identity domain

Lu Baolu
2024-05-29T05:36:29Z

Currently, the identity domain attachment follows the same path as the
paging domain attachment and is subject to the same compatibility checks
as a normal paging domain. However, this level of check is unnecessary
for the identity domain since it only requires the hardware to support
passthrough mode, which is a given for modern hardware.

On the early VT-d platforms, where hardware passthrough mode is not yet
supported, the identity domain is supported by a makeshift paging domain
with the entire system memory 1:1 mapped. For such early hardware, the
appropriate domain type should be returned in device_def_domain_type(),
and the identity domain should be simplified in compatibility checks.

The identity domain workaround in prepare_domain_attach_device() is just
temporary and should be removed once the identity domain is converted to
have its own dedicated attachment path.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
---
drivers/iommu/intel/iommu.c | 18 ++++++++++++++++++
1 file changed, 18 insertions(+)

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index eb8e08699b80..693a6d7c79ed 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -2190,6 +2190,16 @@ static bool device_rmrr_is_relaxable(struct device *dev)
*/
static int device_def_domain_type(struct device *dev)
{
+ struct device_domain_info *info = dev_iommu_priv_get(dev);
+ struct intel_iommu *iommu = info->iommu;
+
+ /*
+ * Hardware does not support the passthrough translation mode.
+ * Always use a dynamaic mapping domain.
+ */
+ if (!ecap_pass_through(iommu->ecap))
+ return IOMMU_DOMAIN_DMA;
+
if (dev_is_pci(dev)) {
struct pci_dev *pdev = to_pci_dev(dev);

@@ -3802,6 +3812,14 @@ int prepare_domain_attach_device(struct iommu_domain *domain,
struct intel_iommu *iommu = info->iommu;
int addr_width;

+ /*
+ * This is a temporary solution as the identity domain attachment
+ * goes through this path as well. It should be removed once the
+ * identity domain has its own attach path.
+ */
+ if (domain->type == IOMMU_DOMAIN_IDENTITY)
+ return ecap_pass_through(iommu->ecap) ? 0 : -EOPNOTSUPP;
+
if (dmar_domain->force_snooping && !ecap_sc_support(iommu->ecap))
return -EINVAL;

--
2.34.1