Re: [PATCH v3 2/4] iommu: Add capability for pre-boot DMA protection

Lu Baolu
2022-04-06T14:21:33Z

On 2022/4/5 18:41, Robin Murphy wrote:
> VT-d's dmar_platform_optin() actually represents a combination of
> properties fairly well standardised by Microsoft as "Pre-boot DMA
> Protection" and "Kernel DMA Protection"[1]. As such, we can provide
> interested consumers with an abstracted capability rather than
> driver-specific interfaces that won't scale. We name it for the former
> aspect since that's what external callers are most likely to be
> interested in; the latter is for the IOMMU layer to handle itself.
>
> [1] https://docs.microsoft.com/en-us/windows-hardware/design/device-experiences/oem-kernel-dma-protection
>
> Suggested-by: Christoph Hellwig <hch@lst.de>
> Reviewed-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>

Reviewed-by: Lu Baolu <baolu.lu@linux.intel.com>

Best regards,
baolu

> ---
> drivers/iommu/intel/iommu.c | 2 ++
> include/linux/iommu.h | 2 ++
> 2 files changed, 4 insertions(+)
>
> diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
> index 255304eb3b1f..49d552a96098 100644
> --- a/drivers/iommu/intel/iommu.c
> +++ b/drivers/iommu/intel/iommu.c
> @@ -4550,6 +4550,8 @@ static bool intel_iommu_capable(struct device *dev, enum iommu_cap cap)
> return domain_update_iommu_snooping(NULL);
> if (cap == IOMMU_CAP_INTR_REMAP)
> return irq_remapping_enabled == 1;
> + if (cap == IOMMU_CAP_PRE_BOOT_PROTECTION)
> + return dmar_platform_optin();
>
> return false;
> }
> diff --git a/include/linux/iommu.h b/include/linux/iommu.h
> index 1fa927e6f1c6..64c02f472f7b 100644
> --- a/include/linux/iommu.h
> +++ b/include/linux/iommu.h
> @@ -107,6 +107,8 @@ enum iommu_cap {
> transactions */
> IOMMU_CAP_INTR_REMAP, /* IOMMU supports interrupt isolation */
> IOMMU_CAP_NOEXEC, /* IOMMU_NOEXEC flag */
> + IOMMU_CAP_PRE_BOOT_PROTECTION, /* Firmware says it used the IOMMU for
> + DMA protection and we should too */
> };
>
> /* These are the possible reserved region types */