Re: [PATCH v1 2/2] iommu/vt-d: Disable PMRs and skip force-IOMMU when TXT TPRs are active

[Baolu Lu]

On 6/3/2026 7:45 PM, Michal Camacho Romero wrote:
> When Intel TXT Protection Regions (TPRs) are present in the DTPR table,
> hardware-level DMA protection is already enforced by the SINIT ACM.
> In this case:
>
> - Skip forcing IOMMU enablement in tboot_force_iommu(), since TPRs
>    already provide DMA protection.
> - Tear down PMRs during intel_iommu_init() when TPRs are active,
>    while PMRs are redundant with TPR-based protection.
> - Call tboot_parse_dtpr_table() from parse_dmar_table() to disable
>    TPR regions early, allowing the kernel to manage DMA protection
>    prior to the OS boot.
>
> Link: https://uefi.org/sites/default/files/resources/633933_Intel_TXT_DMA_Protection_Ranges_rev_0p73.pdf
> Link: https://cdrdv2-public.intel.com/315168/315168_TXT_MLE_DG_rev_017_7.pdf
> Signed-off-by: Michal Camacho Romero <michal.camacho.romero@xxxxxxxxx>
> ---
>   drivers/iommu/intel/dmar.c  | 12 ++++++++++++
>   drivers/iommu/intel/iommu.c |  8 +++++++-
>   2 files changed, 19 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/iommu/intel/dmar.c b/drivers/iommu/intel/dmar.c
> index d33c119a935e..3ab09117c79e 100644
> --- a/drivers/iommu/intel/dmar.c
> +++ b/drivers/iommu/intel/dmar.c
> @@ -635,6 +635,8 @@ static int __init
>   parse_dmar_table(void)
>   {
>   	struct acpi_table_dmar *dmar;
> +	struct acpi_table_dtpr *dtpr;
> +	void                   *txt_heap;

Please avoid using extra whitespace before the variable name. Just use:

	void *txt_heap;

>   	int drhd_count = 0;
>   	int ret;
>   	struct dmar_res_callback cb = {
> @@ -670,6 +672,16 @@ parse_dmar_table(void)
>   		return -EINVAL;
>   	}
>   
> +	dtpr = tboot_get_dtpr_table(&txt_heap);
> +	if (dtpr) {
> +		/* TPR is enabled
> +		 * This will also tell not to establish IOMMU PMRs
> +		 */

Please use the standard kernel multiple-line comment format:

	/*
	 * TPR is enabled. This will also tell not to establish IOMMU
	 * PMRs.
	 */

> +		tboot_parse_dtpr_table(dtpr);
> +		iounmap(txt_heap);
> +	}
> +
> +	txt_heap = NULL;
>   	pr_info("Host address width %d\n", dmar->width + 1);
>   	ret = dmar_walk_dmar_table(dmar, &cb);
>   	if (ret == 0 && drhd_count == 0)
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index 4d0e65bc131d..486693a13dc6 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -2540,6 +2540,12 @@ static __init int tboot_force_iommu(void)
>   	if (!tboot_enabled())
>   		return 0;
>   
> +	/* If TPR is enabled we don't need to force IOMMU,
> +	 * TPR set by SINIT ACM will take care of DMA protection
> +	 */

Ditto.

> +	if (tboot_is_tpr_enabled())
> +		return 0;
> +
>   	if (no_iommu || dmar_disabled)
>   		pr_warn("Forcing Intel-IOMMU to enabled\n");
>   
> @@ -2597,7 +2603,7 @@ int __init intel_iommu_init(void)
>   		 * calling SENTER, but the kernel is expected to reset/tear
>   		 * down the PMRs.
>   		 */
> -		if (intel_iommu_tboot_noforce) {
> +		if (intel_iommu_tboot_noforce || tboot_is_tpr_enabled()) {
>   			for_each_iommu(iommu, drhd)
>   				iommu_disable_protect_mem_regions(iommu);
>   		}

With these nits fixed:

Reviewed-by: Lu Baolu <baolu.lu@xxxxxxxxxxxxxxx>