linux-kernel - Re: [PATCH v12 2/5] iommu: Enhance IOMMU default DMA mode build options

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Message-ID: <a4c85f00-918b-5952-7585-8e1110ac5195@linux.intel.com>
Date:   Sat, 12 Jun 2021 09:21:59 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     John Garry <john.garry@...wei.com>, joro@...tes.org,
        will@...nel.org, dwmw2@...radead.org, robin.murphy@....com
Cc:     baolu.lu@...ux.intel.com, linux-kernel@...r.kernel.org,
        iommu@...ts.linux-foundation.org, linuxarm@...wei.com,
        thunder.leizhen@...wei.com, chenxiang66@...ilicon.com
Subject: Re: [PATCH v12 2/5] iommu: Enhance IOMMU default DMA mode build
 options

On 2021/6/11 20:20, John Garry wrote:
> +config IOMMU_DEFAULT_LAZY
> +	bool "lazy"
> +	help
> +	  Support lazy mode, where for every IOMMU DMA unmap operation, the
> +	  flush operation of IOTLB and the free operation of IOVA are deferred.
> +	  They are only guaranteed to be done before the related IOVA will be
> +	  reused.
> +
> +	  The isolation provided in this mode is not as secure as STRICT mode,
> +	  such that a vulnerable time window may be created between the DMA
> +	  unmap and the mapping finally being torn down in the IOMMU, where the
> +	  device can still access the system memory. However this mode may

" ... and the mappings cached in the IOMMU IOTLB or device TLB finally
being invalidated, where the device probably can still access the memory
which has already been unmapped by the device driver."

Best regards,
baolu