[PATCH] iommu: Update "iommu.strict" documentation

[PATCH] iommu: Update "iommu.strict" documentation

[Robin Murphy]

Consolidating the flush queue logic also meant that the "iommu.strict"
option started taking effect on x86 as well. Make sure we document that.

Fixes: a250c23f15c2 ("iommu: remove DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE")
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---
 Documentation/admin-guide/kernel-parameters.txt | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index cb89dbdedc46..20a32de990ed 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -1987,7 +1987,7 @@
 			  forcing Dual Address Cycle for PCI cards supporting
 			  greater than 32-bit addressing.
 
-	iommu.strict=	[ARM64] Configure TLB invalidation behaviour
+	iommu.strict=	[ARM64, X86] Configure TLB invalidation behaviour
 			Format: { "0" | "1" }
 			0 - Lazy mode.
 			  Request that DMA unmap operations use deferred
@@ -1998,6 +1998,10 @@
 			1 - Strict mode (default).
 			  DMA unmap operations invalidate IOMMU hardware TLBs
 			  synchronously.
+			Note: on x86, the default behaviour depends on the
+			equivalent driver-specific parameters, but a strict
+			mode explicitly specified by either method takes
+			precedence.
 
 	iommu.passthrough=
 			[ARM64, X86] Configure DMA to bypass the IOMMU by default.
-- 
2.25.1

Re: [PATCH] iommu: Update "iommu.strict" documentation

[John Garry]

On 14/06/2021 15:57, Robin Murphy wrote:
> Consolidating the flush queue logic also meant that the "iommu.strict"
> option started taking effect on x86 as well. Make sure we document that.
> 
> Fixes: a250c23f15c2 ("iommu: remove DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE")
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>

I assumed that all bets were off when we use a cmdline param which is 
not "officially" supported.

Anyway, FWIW:
Reviewed-by: John Garry <john.garry@huawei.com>

> ---
>   Documentation/admin-guide/kernel-parameters.txt | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index cb89dbdedc46..20a32de990ed 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1987,7 +1987,7 @@
>   			  forcing Dual Address Cycle for PCI cards supporting
>   			  greater than 32-bit addressing.
>   
> -	iommu.strict=	[ARM64] Configure TLB invalidation behaviour
> +	iommu.strict=	[ARM64, X86] Configure TLB invalidation behaviour
>   			Format: { "0" | "1" }
>   			0 - Lazy mode.
>   			  Request that DMA unmap operations use deferred

Re: [PATCH] iommu: Update "iommu.strict" documentation

[Lu Baolu]

On 6/14/21 10:57 PM, Robin Murphy wrote:
> Consolidating the flush queue logic also meant that the "iommu.strict"
> option started taking effect on x86 as well. Make sure we document that.
> 
> Fixes: a250c23f15c2 ("iommu: remove DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE")
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> ---
>   Documentation/admin-guide/kernel-parameters.txt | 6 +++++-
>   1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index cb89dbdedc46..20a32de990ed 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -1987,7 +1987,7 @@
>   			  forcing Dual Address Cycle for PCI cards supporting
>   			  greater than 32-bit addressing.
>   
> -	iommu.strict=	[ARM64] Configure TLB invalidation behaviour
> +	iommu.strict=	[ARM64, X86] Configure TLB invalidation behaviour
>   			Format: { "0" | "1" }
>   			0 - Lazy mode.
>   			  Request that DMA unmap operations use deferred
> @@ -1998,6 +1998,10 @@
>   			1 - Strict mode (default).
>   			  DMA unmap operations invalidate IOMMU hardware TLBs
>   			  synchronously.
> +			Note: on x86, the default behaviour depends on the
> +			equivalent driver-specific parameters, but a strict
> +			mode explicitly specified by either method takes
> +			precedence.
>   
>   	iommu.passthrough=
>   			[ARM64, X86] Configure DMA to bypass the IOMMU by default.
> 

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

Best regards,
baolu

Re: [PATCH] iommu: Update "iommu.strict" documentation

[Joerg Roedel]

On Mon, Jun 14, 2021 at 03:57:26PM +0100, Robin Murphy wrote:
> Consolidating the flush queue logic also meant that the "iommu.strict"
> option started taking effect on x86 as well. Make sure we document that.
> 
> Fixes: a250c23f15c2 ("iommu: remove DOMAIN_ATTR_DMA_USE_FLUSH_QUEUE")
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> ---
>  Documentation/admin-guide/kernel-parameters.txt | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)

Applied, thanks.