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Message-ID: <4bd4b850-720e-bd02-c04d-01013be49456@linux.intel.com>
Date: Fri, 18 Jun 2021 21:11:51 +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,
corbet@....net
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,
linux-doc@...r.kernel.org
Subject: Re: [PATCH v14 3/6] iommu: Enhance IOMMU default DMA mode build
options
On 2021/6/18 19:34, John Garry wrote:
> From: Zhen Lei <thunder.leizhen@...wei.com>
>
> First, add build options IOMMU_DEFAULT_{LAZY|STRICT}, so that we have the
> opportunity to set {lazy|strict} mode as default at build time. Then put
> the two config options in an choice, as they are mutually exclusive.
>
> [jpg: Make choice between strict and lazy only (and not passthrough)]
> Signed-off-by: Zhen Lei <thunder.leizhen@...wei.com>
> Signed-off-by: John Garry <john.garry@...wei.com>
> Reviewed-by: Robin Murphy <robin.murphy@....com>
> ---
> .../admin-guide/kernel-parameters.txt | 3 +-
> drivers/iommu/Kconfig | 40 +++++++++++++++++++
> drivers/iommu/iommu.c | 2 +-
> 3 files changed, 43 insertions(+), 2 deletions(-)
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index 673952379900..a1b7c8526bb5 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -2046,9 +2046,10 @@
> throughput at the cost of reduced device isolation.
> Will fall back to strict mode if not supported by
> the relevant IOMMU driver.
> - 1 - Strict mode (default).
> + 1 - Strict mode.
> DMA unmap operations invalidate IOMMU hardware TLBs
> synchronously.
> + unset - Use value of CONFIG_IOMMU_DEFAULT_{LAZY,STRICT}.
> Note: on x86, the default behaviour depends on the
> equivalent driver-specific parameters, but a strict
> mode explicitly specified by either method takes
> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
> index 1f111b399bca..0327a942fdb7 100644
> --- a/drivers/iommu/Kconfig
> +++ b/drivers/iommu/Kconfig
> @@ -90,6 +90,46 @@ config IOMMU_DEFAULT_PASSTHROUGH
>
> If unsure, say N here.
>
> +choice
> + prompt "IOMMU default DMA IOTLB invalidation mode"
> + depends on IOMMU_DMA
> +
> + default IOMMU_DEFAULT_STRICT
> + help
> + This option allows an IOMMU DMA IOTLB invalidation mode to be
> + chosen at build time, to override the default mode of each ARCH,
> + removing the need to pass in kernel parameters through command line.
> + It is still possible to provide common boot params to override this
> + config.
> +
> + If unsure, keep the default.
> +
> +config IOMMU_DEFAULT_STRICT
> + bool "strict"
> + help
> + For every IOMMU DMA unmap operation, the flush operation of IOTLB and
> + the free operation of IOVA are guaranteed to be done in the unmap
> + function.
> +
> +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 mappings cached in the IOMMU IOTLB or device TLB
> + finally being invalidated, where the device could still access the
> + memory which has already been unmapped by the device driver.
> + However this mode may provide better performance in high throughput
> + scenarios, and is still considerably more secure than passthrough
> + mode or no IOMMU.
> +
> +endchoice
> +
> config OF_IOMMU
> def_bool y
> depends on OF && IOMMU_API
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index cf58949cc2f3..60b1ec42e73b 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -29,7 +29,7 @@ static struct kset *iommu_group_kset;
> static DEFINE_IDA(iommu_group_ida);
>
> static unsigned int iommu_def_domain_type __read_mostly;
> -static bool iommu_dma_strict __read_mostly = true;
> +static bool iommu_dma_strict __read_mostly = IS_ENABLED(CONFIG_IOMMU_DEFAULT_STRICT);
> static u32 iommu_cmd_line __read_mostly;
>
> struct iommu_group {
>
Reviewed-by: Lu Baolu <baolu.lu@...ux.intel.com>
Best regards,
baolu
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