iommu/vt-d: Avoid panic if iommu init fails in tboot system

"intel_iommu=off" command line is used to disable iommu but iommu is force
enabled in a tboot system for security reason.

However for better performance on high speed network device, a new option
"intel_iommu=tboot_noforce" is introduced to disable the force on.

By default kernel should panic if iommu init fail in tboot for security
reason, but it's unnecessory if we use "intel_iommu=tboot_noforce,off".

Fix the code setting force_on and move intel_iommu_tboot_noforce
from tboot code to intel iommu code.

Fixes: 7304e8f ("iommu/vt-d: Correctly disable Intel IOMMU force on")
Signed-off-by: Zhenzhong Duan <zhenzhong.duan@gmail.com>
Tested-by: Lukasz Hawrylko <lukasz.hawrylko@linux.intel.com>
Acked-by: Lu Baolu <baolu.lu@linux.intel.com>
Link: https://lore.kernel.org/r/20201110071908.3133-1-zhenzhong.duan@gmail.com
Signed-off-by: Will Deacon <will@kernel.org>

Author: Zhenzhong Duan

arch/x86/kernel/tboot.c

@@ -514,9 +514,6 @@ int tboot_force_iommu(void)
 	if (!tboot_enabled())
 		return 0;
 
-	if (intel_iommu_tboot_noforce)
-		return 1;
-
 	if (no_iommu || swiotlb || dmar_disabled)
 		pr_warn("Forcing Intel-IOMMU to enabled\n");
 

drivers/iommu/intel/iommu.c

@@ -179,7 +179,7 @@ static int rwbf_quirk;
  * (used when kernel is launched w/ TXT)
  */
 static int force_on = 0;
-int intel_iommu_tboot_noforce;
+static int intel_iommu_tboot_noforce;
 static int no_platform_optin;
 
 #define ROOT_ENTRY_NR (VTD_PAGE_SIZE/sizeof(struct root_entry))
@@ -4885,7 +4885,8 @@ int __init intel_iommu_init(void)
 	 * Intel IOMMU is required for a TXT/tboot launch or platform
 	 * opt in, so enforce that.
 	 */
-	force_on = tboot_force_iommu() || platform_optin_force_iommu();
+	force_on = (!intel_iommu_tboot_noforce && tboot_force_iommu()) ||
+		    platform_optin_force_iommu();
 
 	if (iommu_init_mempool()) {
 		if (force_on)

include/linux/intel-iommu.h

@@ -798,7 +798,6 @@ extern int iommu_calculate_agaw(struct intel_iommu *iommu);
 extern int iommu_calculate_max_sagaw(struct intel_iommu *iommu);
 extern int dmar_disabled;
 extern int intel_iommu_enabled;
-extern int intel_iommu_tboot_noforce;
 extern int intel_iommu_gfx_mapped;
 #else
 static inline int iommu_calculate_agaw(struct intel_iommu *iommu)