iommu/vt-d: Support the new DMA_REMAP_OPT_OUT flag bit

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Some BIOS already provides config options to expose/hide VT-d units
as a whole to/from system software. A new demand is to allow exposing
VT-d units but requesting system software to disable DMA remapping
while sustaining interrupt remapping. This can be communicated now by
setting the new DMA_REMAP_OPT_OUT flag bit in the DMAR table, as
introduced in VT-d spec v5.2 (section 8.1, DMA Remapping Reporting
Structure).

Introduce a new off policy (DMAR_FW_OFF) for DMA_REMAP_OPT_OUT. As
the strongest off policy, it cannot be overridden by user opts or
any force_on types. If tboot is enabled in the meantime, kernel will
panic. It is user responsibility to configure BIOS properly.

One cleanup is left for future - the DMAR flag is parsed multiple
times, in detect_intel_iommu(), dmar_platform_optin() (which can be
called at run-time), etc. Caching it is a cleaner way.

Signed-off-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Signed-off-by: Joerg Roedel <joerg.roedel@amd.com>

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This commit is contained in:

Kevin Tian 2026-08-05 07:43:07 +08:00 • committed by Joerg Roedel

parent 3f29c94eca

commit 1c677d8a2c

3 changed files with 29 additions and 10 deletions

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34

drivers/iommu/intel/dmar.c

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4

drivers/iommu/intel/iommu.h

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1

include/linux/dmar.h

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