[PATCH] iommu/vt-d: avoid unnecessory panic if iommu init fail in tboot

[Zhenzhong Duan <zhenzhong.duan@gmail.com>]

"intel_iommu=off" command line is used to disable iommu and iommu is force
enabled in a tboot system. Meanwhile "intel_iommu=tboot_noforce,off"
could be used to force disable iommu in tboot for better performance.

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 it by return 0 in tboot_force_iommu() so that force_on is not set.

Fixes: 7304e8f28bb2 ("iommu/vt-d: Correctly disable Intel IOMMU force on")
Signed-off-by: Zhenzhong Duan <zhenzhong.duan@gmail.com>
---
 arch/x86/kernel/tboot.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/arch/x86/kernel/tboot.c b/arch/x86/kernel/tboot.c
index 992fb1415c0f..9fd4d162b331 100644
--- a/arch/x86/kernel/tboot.c
+++ b/arch/x86/kernel/tboot.c
@@ -511,12 +511,9 @@ struct acpi_table_header *tboot_get_dmar_table(struct acpi_table_header *dmar_tb
 
 int tboot_force_iommu(void)
 {
-	if (!tboot_enabled())
+	if (!tboot_enabled() || intel_iommu_tboot_noforce)
 		return 0;
 
-	if (intel_iommu_tboot_noforce)
-		return 1;
-
 	if (no_iommu || swiotlb || dmar_disabled)
 		pr_warn("Forcing Intel-IOMMU to enabled\n");
 
-- 
2.25.1