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

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Date:   Wed, 6 Apr 2022 18:28:01 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Robin Murphy <robin.murphy@....com>, joro@...tes.org,
        andreas.noever@...il.com, michael.jamet@...el.com,
        mika.westerberg@...ux.intel.com, YehezkelShB@...il.com
Cc:     baolu.lu@...ux.intel.com, iommu@...ts.linux-foundation.org,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org,
        mario.limonciello@....com, hch@....de
Subject: Re: [PATCH v3 2/4] iommu: Add capability for pre-boot DMA protection

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@....de>
> Reviewed-by: Christoph Hellwig <hch@....de>
> Signed-off-by: Robin Murphy <robin.murphy@....com>

Reviewed-by: Lu Baolu <baolu.lu@...ux.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 */