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iommu/vt-d: Fix no_iommu to disable platform opt-in

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If user explicitly requests to disable iommu (via "iommu=off" or
"intel_iommu=off"), there is no reason to force enabling it due
to platform opt-in (for external-facing devices). User should be
aware of any security implication of doing so.

"intel_iommu=off" implements this policy by setting no_platform_optin
to skip platform opt-in in platform_optin_force_iommu().

However, "iommu=off" (no_iommu=1) doesn't set no_platform_optin
hence is broken in this aspect:

  - detect_intel_iommu() doesn't request ACS if no_iommu=1
  - platform_optin_force_iommu() forces iommu on if external-facing
    devices exist and no_platform_optin is not set

This leads to a bad configuration with ACS disabled while DMA
remapping is enabled.

Instead of setting no_platform_optin (will soon be removed) for
no_iommu=1, directly check no_iommu in platform_optin_force_iommu().

Fixes: 89a6079df7 ("iommu/vt-d: Force IOMMU on for platform opt in hint")
Cc: stable@vger.kernel.org
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>
This commit is contained in:
Kevin Tian 2026-08-05 07:42:59 +08:00 committed by Joerg Roedel
parent 1251ade0e3
commit 219cc978d6
1 changed files with 3 additions and 3 deletions
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6
drivers/iommu/intel/iommu.c
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@ -2484,10 +2484,11 @@ static bool has_external_pci(void)
static int __init platform_optin_force_iommu(void)
{
if (!dmar_platform_optin() || no_platform_optin || !has_external_pci())
if (no_iommu || !dmar_platform_optin() || no_platform_optin ||
!has_external_pci())
return 0;
if (no_iommu || dmar_disabled)
if (dmar_disabled)
pr_info("Intel-IOMMU force enabled due to platform opt in\n");
/*
@ -2498,7 +2499,6 @@ static int __init platform_optin_force_iommu(void)
iommu_set_default_passthrough(false);
dmar_disabled = 0;
no_iommu = 0;
return 1;
}