RE: [PATCH] iommu/amd: Add amd_iommu=force_enable option

["Deucher, Alexander" <Alexander.Deucher@amd.com>]

[AMD Public Use]

> -----Original Message-----
> From: Joerg Roedel <joro@8bytes.org>
> Sent: Thursday, April 22, 2021 9:07 AM
> To: iommu@lists.linux-foundation.org
> Cc: Joerg Roedel <joro@8bytes.org>; Will Deacon <will@kernel.org>;
> Deucher, Alexander <Alexander.Deucher@amd.com>;
> d1nuc0m@protonmail.com; linux-doc@vger.kernel.org; linux-
> kernel@vger.kernel.org; Joerg Roedel <jroedel@suse.de>
> Subject: [PATCH] iommu/amd: Add amd_iommu=force_enable option
> 
> From: Joerg Roedel <jroedel@suse.de>
> 
> Add this option to enable the IOMMU on platforms like AMD Stoney, where
> the kernel usually disables it because it may cause problems in some
> scenarios.
> 
> Signed-off-by: Joerg Roedel <jroedel@suse.de>

Acked-by: Alex Deucher <alexander.deucher@amd.com>

> ---
>  Documentation/admin-guide/kernel-parameters.txt | 3 +++
>  drivers/iommu/amd/init.c                        | 7 +++++++
>  2 files changed, 10 insertions(+)
> 
> diff --git a/Documentation/admin-guide/kernel-parameters.txt
> b/Documentation/admin-guide/kernel-parameters.txt
> index 04545725f187..c9573f726707 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -303,6 +303,9 @@
>  					  allowed anymore to lift isolation
>  					  requirements as needed. This
> option
>  					  does not override iommu=pt
> +			force_enable - Force enable the IOMMU on
> platforms known
> +				       to be buggy with IOMMU enabled. Use
> this
> +				       option with care.
> 
>  	amd_iommu_dump=	[HW,X86-64]
>  			Enable AMD IOMMU driver option to dump the ACPI
> table diff --git a/drivers/iommu/amd/init.c b/drivers/iommu/amd/init.c
> index 321f5906e6ed..3e2295d3b3e2 100644
> --- a/drivers/iommu/amd/init.c
> +++ b/drivers/iommu/amd/init.c
> @@ -155,6 +155,7 @@ static int amd_iommu_xt_mode =
> IRQ_REMAP_XAPIC_MODE;
> 
>  static bool amd_iommu_detected;
>  static bool __initdata amd_iommu_disabled;
> +static bool __initdata amd_iommu_force_enable;
>  static int amd_iommu_target_ivhd_type;
> 
>  u16 amd_iommu_last_bdf;			/* largest PCI device id we
> have
> @@ -2882,6 +2883,9 @@ static bool detect_ivrs(void)
> 
>  	acpi_put_table(ivrs_base);
> 
> +	if (amd_iommu_force_enable)
> +		goto out;
> +
>  	/* Don't use IOMMU if there is Stoney Ridge graphics */
>  	for (i = 0; i < 32; i++) {
>  		u32 pci_id;
> @@ -2893,6 +2897,7 @@ static bool detect_ivrs(void)
>  		}
>  	}
> 
> +out:
>  	/* Make sure ACS will be enabled during PCI probe */
>  	pci_request_acs();
> 
> @@ -3148,6 +3153,8 @@ static int __init parse_amd_iommu_options(char
> *str)
>  	for (; *str; ++str) {
>  		if (strncmp(str, "fullflush", 9) == 0)
>  			amd_iommu_unmap_flush = true;
> +		if (strncmp(str, "force_enable", 12) == 0)
> +			amd_iommu_force_enable = true;
>  		if (strncmp(str, "off", 3) == 0)
>  			amd_iommu_disabled = true;
>  		if (strncmp(str, "force_isolation", 15) == 0)
> --
> 2.31.1