Re: [PATCH 6/9] iommu/vt-d: Call dmar_can_force_on() for tboot optin

[Baolu Lu <baolu.lu@linux.intel.com>]

On 6/4/2026 1:15 PM, Kevin Tian wrote:
> So the policy of requesting ACS in detect_intel_iommu() is consistent
> with that in tboot_force_iommu().
> 
> Though tboot is the strongest override so far, add a panic() in case
> dmar_can_force_on() may return false due to future extensions.
> 
> No functional impact at this point.
> 
> Signed-off-by: Kevin Tian <kevin.tian@intel.com>
> ---
>   drivers/iommu/intel/iommu.c | 11 +++++++----
>   1 file changed, 7 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index edf01261a41d..ed227de6d0ba 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -2544,12 +2544,16 @@ static int __init probe_acpi_namespace_devices(void)
>   
>   static __init int tboot_force_iommu(void)
>   {
> -	if (!tboot_enabled())
> +	if (!tboot_enabled() || intel_iommu_tboot_noforce)

Hmm, it looks a bit strange here. The core design philosophy is that the
trusted boot environment takes priority over user options. However,
checking intel_iommu_tboot_noforce at the very top means a user
option (intel_iommu=tboot_noforce) is successfully overriding tboot.

Is this an exception? If so, it might be worth adding a brief comment
clarifying why `tboot_noforce` is allowed to bypass the priority?

>   		return 0;
>   
> -	if (no_iommu || dmar_disabled)
> +	if (!dmar_can_force_on(DMAR_FORCEON_TBOOT))
> +		panic("tboot: Failed to force IOMMU on\n");
> +
> +	if (dmar_is_disabled())
>   		pr_warn("Forcing Intel-IOMMU to enabled\n");
>   
> +	dmar_state = DMAR_ENABLED_FORCE;
>   	dmar_disabled = 0;
>   	no_iommu = 0;
>   
> @@ -2566,8 +2570,7 @@ int __init intel_iommu_init(void)
>   	 * Intel IOMMU is required for a TXT/tboot launch or platform
>   	 * opt in, so enforce that.
>   	 */
> -	force_on = (!intel_iommu_tboot_noforce && tboot_force_iommu()) ||
> -		    platform_optin_force_iommu();
> +	force_on = tboot_force_iommu() || platform_optin_force_iommu();
>   
>   	down_write(&dmar_global_lock);
>   	if (dmar_table_init()) {

Thanks,
baolu