Re: [PATCH 7/9] iommu/vt-d: Remove the 'force_on' variable

[Baolu Lu]

On 6/4/2026 1:15 PM, Kevin Tian wrote:
> The force_on variable is now redundant - same information captured
> by "dmar_state == DMAR_ENABLED_FORCE". Replace all force_on checks
> with dmar_is_force_on().
>
> Signed-off-by: Kevin Tian <kevin.tian@xxxxxxxxx>
> ---
>   drivers/iommu/intel/iommu.c | 34 +++++++++++++++-------------------
>   drivers/iommu/intel/iommu.h |  5 +++++
>   2 files changed, 20 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index ed227de6d0ba..d05ae36eda70 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -53,10 +53,9 @@ static int rwbf_quirk;
>   #define rwbf_required(iommu)	(rwbf_quirk || cap_rwbf((iommu)->cap))
>   
>   /*
> - * set to 1 to panic kernel if can't successfully enable VT-d
> + * set to 1 to avoid kernel panic if can't successfully enable VT-d
>    * (used when kernel is launched w/ TXT)
>    */

It might be cleaner to replace it entirely with a new comment. For
example:

/*
 * Skip forcing iommu enablement and avoid tboot-related kernel panics
 * during initialization when set to 1 (via intel_iommu=tboot_noforce).
 */
int intel_iommu_tboot_noforce;

> -static int force_on = 0;
>   int intel_iommu_tboot_noforce;
>   
>   #define ROOT_ENTRY_NR (VTD_PAGE_SIZE/sizeof(struct root_entry))
> @@ -1708,7 +1707,7 @@ static int __init init_dmars(void)
>   			 * we always have to disable PMRs or DMA may fail on
>   			 * this device
>   			 */
> -			if (force_on)
> +			if (dmar_is_force_on())
>   				iommu_disable_protect_mem_regions(iommu);
>   			continue;
>   		}
> @@ -1800,7 +1799,7 @@ static int init_iommu_hw(void)
>   			 * we always have to disable PMRs or DMA may fail on
>   			 * this device
>   			 */
> -			if (force_on)
> +			if (dmar_is_force_on())
>   				iommu_disable_protect_mem_regions(iommu);
>   			continue;
>   		}
> @@ -1861,7 +1860,7 @@ static void iommu_resume(void *data)
>   	unsigned long flag;
>   
>   	if (init_iommu_hw()) {
> -		if (force_on)
> +		if (dmar_is_force_on())
>   			panic("tboot: IOMMU setup failed, DMAR can not resume!\n");
>   		else
>   			WARN(1, "IOMMU setup failed, DMAR can not resume!\n");
> @@ -2129,7 +2128,7 @@ static int intel_iommu_add(struct dmar_drhd_unit *dmaru)
>   		/*
>   		 * we always have to disable PMRs or DMA may fail on this device
>   		 */
> -		if (force_on)
> +		if (dmar_is_force_on())
>   			iommu_disable_protect_mem_regions(iommu);
>   		return 0;
>   	}
> @@ -2482,13 +2481,13 @@ static bool has_external_pci(void)
>   	return false;
>   }
>   
> -static int __init platform_optin_force_iommu(void)
> +static void __init platform_optin_force_iommu(void)
>   {
>   	if (!dmar_platform_optin() || !dmar_can_force_on(DMAR_FORCEON_PLATFORM))
> -		return 0;
> +		return;
>   
>   	if (!has_external_pci())
> -		return 0;
> +		return;
>   
>   	/*
>   	 * If Intel-IOMMU is disabled by default, we will apply identity
> @@ -2501,8 +2500,6 @@ static int __init platform_optin_force_iommu(void)
>   
>   	dmar_state = DMAR_ENABLED_FORCE;
>   	dmar_disabled = 0;
> -
> -	return 1;
>   }
>   
>   static int __init probe_acpi_namespace_devices(void)
> @@ -2542,10 +2539,10 @@ static int __init probe_acpi_namespace_devices(void)
>   	return 0;
>   }
>   
> -static __init int tboot_force_iommu(void)
> +static __init void tboot_force_iommu(void)
>   {
>   	if (!tboot_enabled() || intel_iommu_tboot_noforce)
> -		return 0;
> +		return;
>   
>   	if (!dmar_can_force_on(DMAR_FORCEON_TBOOT))
>   		panic("tboot: Failed to force IOMMU on\n");
> @@ -2556,8 +2553,6 @@ static __init int tboot_force_iommu(void)
>   	dmar_state = DMAR_ENABLED_FORCE;
>   	dmar_disabled = 0;
>   	no_iommu = 0;
> -
> -	return 1;
>   }
>   
>   int __init intel_iommu_init(void)
> @@ -2570,17 +2565,18 @@ 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();
> +	tboot_force_iommu();
> +	platform_optin_force_iommu();
>   
>   	down_write(&dmar_global_lock);
>   	if (dmar_table_init()) {
> -		if (force_on)
> +		if (dmar_is_force_on())
>   			panic("tboot: Failed to initialize DMAR table\n");
>   		goto out_free_dmar;
>   	}
>   
>   	if (dmar_dev_scope_init() < 0) {
> -		if (force_on)
> +		if (dmar_is_force_on())
>   			panic("tboot: Failed to initialize DMAR device scope\n");
>   		goto out_free_dmar;
>   	}
> @@ -2634,7 +2630,7 @@ int __init intel_iommu_init(void)
>   
>   	ret = init_dmars();
>   	if (ret) {
> -		if (force_on)
> +		if (dmar_is_force_on())
>   			panic("tboot: Failed to initialize DMARs\n");
>   		pr_err("Initialization failed\n");
>   		goto out_free_dmar;
> diff --git a/drivers/iommu/intel/iommu.h b/drivers/iommu/intel/iommu.h
> index 1acc393dafce..6b4e47f2f245 100644
> --- a/drivers/iommu/intel/iommu.h
> +++ b/drivers/iommu/intel/iommu.h
> @@ -1383,6 +1383,11 @@ static inline bool dmar_is_disabled(void)
>   	return dmar_state < 0;
>   }
>   
> +static inline bool dmar_is_force_on(void)
> +{
> +	return dmar_state == DMAR_ENABLED_FORCE;
> +}

This helper is only meaningful after

tboot_force_iommu();
platform_optin_force_iommu();

have been called. It would be better to add a brief comment about this?

> +
>   bool dmar_can_force_on(enum dmar_force_on force_on);
>   
>   extern int dmar_disabled;

Thanks,
baolu