From: Lu Baolu <baolu.lu@linux.intel.com>

The Intel TDX Connect Architecture Specification defines some enhancements
for the VT-d architecture to introduce IOMMU support for TEE-IO requests.
Section 2.2, 'Trusted DMA' states that:

"I/O TLB and DID Isolation – When IOMMU is enabled to support TDX
Connect, the IOMMU restricts the VMM’s DID setting, reserving the MSB bit
for the TDX module. The TDX module always sets this reserved bit on the
trusted DMA table. IOMMU tags IOTLB, PASID cache, and context entries to
indicate whether they were created from TEE-IO transactions, ensuring
isolation between TEE and non-TEE requests in translation caches."

Reserve the MSB in the domain ID for the TDX module's use if the
enhancement is required, which is detected if the ECAP.TDXCS bit in the
VT-d extended capability register is set and the TVM Usable field of the
ACPI KEYP table is set.

Co-developed-by: Xu Yilun <yilun.xu@linux.intel.com>
Signed-off-by: Xu Yilun <yilun.xu@linux.intel.com>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
---
 drivers/iommu/intel/iommu.h |  1 +
 drivers/iommu/intel/dmar.c  | 52 ++++++++++++++++++++++++++++++++++++-
 2 files changed, 52 insertions(+), 1 deletion(-)

diff --git a/drivers/iommu/intel/iommu.h b/drivers/iommu/intel/iommu.h
index 4a21ab6a311d..0c2b4e38dee7 100644
--- a/drivers/iommu/intel/iommu.h
+++ b/drivers/iommu/intel/iommu.h
@@ -192,6 +192,7 @@
  */
 
 #define ecap_pms(e)		(((e) >> 51) & 0x1)
+#define ecap_tdxc(e)		(((e) >> 50) & 0x1)
 #define ecap_rps(e)		(((e) >> 49) & 0x1)
 #define ecap_smpwc(e)		(((e) >> 48) & 0x1)
 #define ecap_flts(e)		(((e) >> 47) & 0x1)
diff --git a/drivers/iommu/intel/dmar.c b/drivers/iommu/intel/dmar.c
index 93efd1a5dc5b..4f9571eee1d4 100644
--- a/drivers/iommu/intel/dmar.c
+++ b/drivers/iommu/intel/dmar.c
@@ -1033,6 +1033,56 @@ static int map_iommu(struct intel_iommu *iommu, struct dmar_drhd_unit *drhd)
 	return err;
 }
 
+static int keyp_config_unit_tvm_usable(union acpi_subtable_headers *header,
+				       void *arg, const unsigned long end)
+{
+	struct acpi_keyp_config_unit *acpi_cu =
+		(struct acpi_keyp_config_unit *)&header->keyp;
+	int *tvm_usable = arg;
+
+	if (acpi_cu->flags & ACPI_KEYP_F_TVM_USABLE)
+		*tvm_usable = 1;
+
+	return 0;
+}
+
+static bool platform_is_tdxc_enhanced(void)
+{
+	static int tvm_usable = -1;
+	int ret;
+
+	/* only need to parse once */
+	if (tvm_usable != -1)
+		return !!tvm_usable;
+
+	tvm_usable = 0;
+	ret = acpi_table_parse_keyp(ACPI_KEYP_TYPE_CONFIG_UNIT,
+				    keyp_config_unit_tvm_usable, &tvm_usable);
+	if (ret < 0)
+		tvm_usable = 0;
+
+	return !!tvm_usable;
+}
+
+static unsigned long iommu_max_domain_id(struct intel_iommu *iommu)
+{
+	unsigned long ndoms = cap_ndoms(iommu->cap);
+
+	/*
+	 * Intel TDX Connect Architecture Specification, Section 2.2 Trusted DMA
+	 *
+	 * When IOMMU is enabled to support TDX Connect, the IOMMU restricts
+	 * the VMM’s DID setting, reserving the MSB bit for the TDX module. The
+	 * TDX module always sets this reserved bit on the trusted DMA table.
+	 */
+	if (ecap_tdxc(iommu->ecap) && platform_is_tdxc_enhanced()) {
+		pr_info_once("Most Significant Bit of domain ID reserved.\n");
+		return ndoms >> 1;
+	}
+
+	return ndoms;
+}
+
 static int alloc_iommu(struct dmar_drhd_unit *drhd)
 {
 	struct intel_iommu *iommu;
@@ -1099,7 +1149,7 @@ static int alloc_iommu(struct dmar_drhd_unit *drhd)
 	spin_lock_init(&iommu->lock);
 	ida_init(&iommu->domain_ida);
 	mutex_init(&iommu->did_lock);
-	iommu->max_domain_id = cap_ndoms(iommu->cap);
+	iommu->max_domain_id = iommu_max_domain_id(iommu);
 
 	ver = readl(iommu->reg + DMAR_VER_REG);
 	pr_info("%s: reg_base_addr %llx ver %d:%d cap %llx ecap %llx\n",
-- 
2.25.1

Hi Xu,

kernel test robot noticed the following build warnings:

[auto build test WARNING on 11439c4635edd669ae435eec308f4ab8a0804808]

url:    https://github.com/intel-lab-lkp/linux/commits/Xu-Yilun/x86-tdx-Move-all-TDX-error-defines-into-asm-shared-tdx_errno-h/20260328-151524
base:   11439c4635edd669ae435eec308f4ab8a0804808
patch link:    https://lore.kernel.org/r/20260327160132.2946114-20-yilun.xu%40linux.intel.com
patch subject: [PATCH v2 19/31] iommu/vt-d: Reserve the MSB domain ID bit for the TDX module
config: x86_64-defconfig (https://download.01.org/0day-ci/archive/20260329/202603290317.BVIn0aoy-lkp@intel.com/config)
compiler: gcc-14 (Debian 14.2.0-19) 14.2.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260329/202603290317.BVIn0aoy-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202603290317.BVIn0aoy-lkp@intel.com/

All warnings (new ones prefixed by >>, old ones prefixed by <<):

>> WARNING: modpost: vmlinux: section mismatch in reference: alloc_iommu.cold+0x49 (section: .text.unlikely) -> acpi_table_parse_keyp (section: .init.text)

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Hi Xu,

kernel test robot noticed the following build warnings:

[auto build test WARNING on 11439c4635edd669ae435eec308f4ab8a0804808]

url:    https://github.com/intel-lab-lkp/linux/commits/Xu-Yilun/x86-tdx-Move-all-TDX-error-defines-into-asm-shared-tdx_errno-h/20260328-151524
base:   11439c4635edd669ae435eec308f4ab8a0804808
patch link:    https://lore.kernel.org/r/20260327160132.2946114-20-yilun.xu%40linux.intel.com
patch subject: [PATCH v2 19/31] iommu/vt-d: Reserve the MSB domain ID bit for the TDX module
config: i386-randconfig-141-20260328 (https://download.01.org/0day-ci/archive/20260329/202603290006.za7iiDgF-lkp@intel.com/config)
compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
smatch: v0.5.0-9004-gb810ac53
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260329/202603290006.za7iiDgF-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202603290006.za7iiDgF-lkp@intel.com/

All warnings (new ones prefixed by >>, old ones prefixed by <<):

>> WARNING: modpost: vmlinux: section mismatch in reference: iommu_max_domain_id+0x55 (section: .text.iommu_max_domain_id) -> acpi_table_parse_keyp (section: .init.text)

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

On 3/29/26 00:57, kernel test robot wrote:
> kernel test robot noticed the following build warnings:
> 
> [auto build test WARNING on 11439c4635edd669ae435eec308f4ab8a0804808]
> 
> url:https://github.com/intel-lab-lkp/linux/commits/Xu-Yilun/x86-tdx-Move- 
> all-TDX-error-defines-into-asm-shared-tdx_errno-h/20260328-151524
> base:   11439c4635edd669ae435eec308f4ab8a0804808
> patch link:https://lore.kernel.org/r/20260327160132.2946114-20- 
> yilun.xu%40linux.intel.com
> patch subject: [PATCH v2 19/31] iommu/vt-d: Reserve the MSB domain ID bit for the TDX module
> config: i386-randconfig-141-20260328 (https://download.01.org/0day-ci/archive/20260329/202603290006.za7iiDgF- 
> lkp@intel.com/config)
> compiler: clang version 20.1.8 (https://github.com/llvm/llvm-project 87f0227cb60147a26a1eeb4fb06e3b505e9c7261)
> smatch: v0.5.0-9004-gb810ac53
> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20260329/202603290006.za7iiDgF- 
> lkp@intel.com/reproduce)
> 
> If you fix the issue in a separate patch/commit (i.e. not just a new version of
> the same patch/commit), kindly add following tags
> | Reported-by: kernel test robot<lkp@intel.com>
> | Closes:https://lore.kernel.org/oe-kbuild-all/202603290006.za7iiDgF-lkp@intel.com/
> 
> All warnings (new ones prefixed by >>, old ones prefixed by <<):
> 
>>> WARNING: modpost: vmlinux: section mismatch in reference: iommu_max_domain_id+0x55 (section: .text.iommu_max_domain_id) -> acpi_table_parse_keyp (section: .init.text)


acpi_table_parse_keyp() is marked as __init. But this patch causes the
intel iommu driver to call it from a runtime function.

int __init_or_acpilib
acpi_table_parse_keyp(enum acpi_keyp_type id,
                       acpi_tbl_entry_handler_arg handler_arg, void *arg)
{
         return __acpi_table_parse_entries(ACPI_SIG_KEYP,
                                           sizeof(struct 
acpi_table_keyp), id,
                                           NULL, handler_arg, arg, 0);
}

One way to solve this might be parsing the table once in the __init
context and store the result in variable that could be used after boot.

How about the following additional change (untested)?

diff --git a/drivers/iommu/intel/dmar.c b/drivers/iommu/intel/dmar.c
index 097c4a90302f..0b384a58a3a0 100644
--- a/drivers/iommu/intel/dmar.c
+++ b/drivers/iommu/intel/dmar.c
@@ -63,6 +63,7 @@ LIST_HEAD(dmar_drhd_units);
  struct acpi_table_header * __initdata dmar_tbl;
  static int dmar_dev_scope_status = 1;
  static DEFINE_IDA(dmar_seq_ids);
+static bool tdx_tvm_usable __ro_after_init;

  static int alloc_iommu(struct dmar_drhd_unit *drhd);
  static void free_iommu(struct intel_iommu *iommu);
@@ -915,6 +916,17 @@ dmar_validate_one_drhd(struct acpi_dmar_header 
*entry, void *arg)
  	return 0;
  }

+static void __init intel_iommu_check_tdxc_enhancement(void)
+{
+	int tvm_usable = 0;
+	int ret;
+
+	ret = acpi_table_parse_keyp(ACPI_KEYP_TYPE_CONFIG_UNIT,
+				    keyp_config_unit_tvm_usable, &tvm_usable);
+	if (ret >= 0)
+		tdx_tvm_usable = !!tvm_usable;
+}
+
  void __init detect_intel_iommu(void)
  {
  	int ret;
@@ -923,6 +935,8 @@ void __init detect_intel_iommu(void)
  		.ignore_unhandled = true,
  	};

+	intel_iommu_check_tdxc_enhancement();
+
  	down_write(&dmar_global_lock);
  	ret = dmar_table_detect();
  	if (!ret)
@@ -1046,24 +1060,6 @@ static int keyp_config_unit_tvm_usable(union 
acpi_subtable_headers *header,
  	return 0;
  }

-static bool platform_is_tdxc_enhanced(void)
-{
-	static int tvm_usable = -1;
-	int ret;
-
-	/* only need to parse once */
-	if (tvm_usable != -1)
-		return !!tvm_usable;
-
-	tvm_usable = 0;
-	ret = acpi_table_parse_keyp(ACPI_KEYP_TYPE_CONFIG_UNIT,
-				    keyp_config_unit_tvm_usable, &tvm_usable);
-	if (ret < 0)
-		tvm_usable = 0;
-
-	return !!tvm_usable;
-}
-
  static unsigned long iommu_max_domain_id(struct intel_iommu *iommu)
  {
  	unsigned long ndoms = cap_ndoms(iommu->cap);
@@ -1075,7 +1071,7 @@ static unsigned long iommu_max_domain_id(struct 
intel_iommu *iommu)
  	 * the VMM’s DID setting, reserving the MSB bit for the TDX module. The
  	 * TDX module always sets this reserved bit on the trusted DMA table.
  	 */
-	if (ecap_tdxc(iommu->ecap) && platform_is_tdxc_enhanced()) {
+	if (ecap_tdxc(iommu->ecap) && tdx_tvm_usable) {
  		pr_info_once("Most Significant Bit of domain ID reserved.\n");
  		return ndoms >> 1;
  	}

Thanks,
baolu