linux-kernel - Re: [PATCH] AMD IOMMU: revert "x86, AMD IOMMU: honor iommu=off instead of amd

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Message-ID: <20080922140749.GY24392@amd.com>
Date:	Mon, 22 Sep 2008 16:07:49 +0200
From:	Joerg Roedel <joerg.roedel@....com>
To:	FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
CC:	mingo@...e.hu, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] AMD IOMMU: revert "x86, AMD IOMMU: honor iommu=off instead of amd_iommu=off"

On Mon, Sep 22, 2008 at 10:35:08PM +0900, FUJITA Tomonori wrote:
> This is against tip/x86/iommu.
> 
> =
> From: FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
> Subject: [PATCH] AMD IOMMU: revert "x86, AMD IOMMU: honor iommu=off instead of amd_iommu=off"
> 
> This reverts:
> 
> commit 8b14518fadd9d5915827d86d5c10e602fedf042e
> Author: Joerg Roedel <joerg.roedel@....com>
> Date:   Thu Jul 3 19:35:09 2008 +0200
> 
>     x86, AMD IOMMU: honor iommu=off instead of amd_iommu=off
> 
>     This patch removes the amd_iommu=off kernel parameter and honors the generic
> 
>     iommu=off parameter for the same purpose.
> 
> 
> The above commit is wrong.

It isn't. The user normally don't care about the type of IOMMU in the
system. So disabling it with iommu=off is the right way. To achieve what
you want its better to add iommu=gart and iommu=amd to the option
parser. This will be consistent with Calgary and SWIOTLB too.

> 
> amd_iommu=off kernel parameter and the generic iommu=off parameter
> don't have the same purpose.
> 
> Intel IOMMU also has 'off' option as Intel IOMMU specific parameter
> (intel_iommu=off) like AMD IOMMU had. intel_iommu=off parameter
> for disabling Intel IOMMU.
> 
> The generic iommu=off parameter means that the kernel doesn't use any
> kind of IOMMU, including SWIOTLB (as documented). So you can't use the
> generic iommu=off parameter to disable hardware IOMMU if you use a box
> with max_pfn > MAX_DMA32_PFN. It's is a critical difference.
> 
> Seems that amd_iommu=off parameter worked in the exact same way as
> intel_iommu=off works (though I might be wrong since I can't confirm
> this with AMD IOMMU). So the above commit removed the useful feature
> to disalbe AMD IOMMU safely.
> 
> I'm not sure what the maintainer wanted to do with the commit so I
> can't say that the commit (to remove the above feature) is a bug or
> regression. I'll leave this issue to the maintainer but at least the
> description of how the IOMMU options works is wrong.
> 
> Note that this patch is not a simple revert patch due to some
> modifications after the above commit.
> 
> Signed-off-by: FUJITA Tomonori <fujita.tomonori@....ntt.co.jp>
> ---
>  Documentation/kernel-parameters.txt |    1 +
>  arch/x86/kernel/amd_iommu_init.c    |    8 ++++++--
>  2 files changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> index 569527e..feddbb7 100644
> --- a/Documentation/kernel-parameters.txt
> +++ b/Documentation/kernel-parameters.txt
> @@ -281,6 +281,7 @@ and is between 256 and 4096 characters. It is defined in the file
>  	amd_iommu=	[HW,X86-84]
>  			Pass parameters to the AMD IOMMU driver in the system.
>  			Possible values are:
> +			off     - disable AMD IOMMU driver
>  			isolate - enable device isolation (each device, as far
>  			          as possible, will get its own protection
>  			          domain)
> diff --git a/arch/x86/kernel/amd_iommu_init.c b/arch/x86/kernel/amd_iommu_init.c
> index db0c83a..a71beb4 100644
> --- a/arch/x86/kernel/amd_iommu_init.c
> +++ b/arch/x86/kernel/amd_iommu_init.c
> @@ -115,6 +115,7 @@ struct ivmd_header {
>  } __attribute__((packed));
>  
>  static int __initdata amd_iommu_detected;
> +static int __initdata amd_iommu_disable;
>  
>  u16 amd_iommu_last_bdf;			/* largest PCI device id we have
>  					   to handle */
> @@ -1037,7 +1038,7 @@ int __init amd_iommu_init(void)
>  	int i, ret = 0;
>  
>  
> -	if (no_iommu) {
> +	if (no_iommu || amd_iommu_disable) {
>  		printk(KERN_INFO "AMD IOMMU disabled by kernel command line\n");
>  		return 0;
>  	}
> @@ -1189,7 +1190,8 @@ static int __init early_amd_iommu_detect(struct acpi_table_header *table)
>  
>  void __init amd_iommu_detect(void)
>  {
> -	if (swiotlb || no_iommu || (iommu_detected && !gart_iommu_aperture))
> +	if (swiotlb || no_iommu || (iommu_detected && !gart_iommu_aperture) ||
> +		amd_iommu_disable)
>  		return;
>  
>  	if (acpi_table_parse("IVRS", early_amd_iommu_detect) == 0) {
> @@ -1212,6 +1214,8 @@ void __init amd_iommu_detect(void)
>  static int __init parse_amd_iommu_options(char *str)
>  {
>  	for (; *str; ++str) {
> +		if (!strncmp(str, "off", 3))
> +			amd_iommu_disable = 1;
>  		if (strncmp(str, "isolate", 7) == 0)
>  			amd_iommu_isolate = 1;
>  	}
> -- 
> 1.5.4.2
> 
> 

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