linux-kernel - Re: [PATCH 10/11] iommu: Disable passthrough mode when SME is active

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Message-ID: <82e00ce5-df71-5b71-cf5d-3de86aa0a1e8@amd.com>
Date:   Tue, 20 Aug 2019 21:18:03 +0000
From:   "Lendacky, Thomas" <Thomas.Lendacky@....com>
To:     Joerg Roedel <joro@...tes.org>
CC:     "corbet@....net" <corbet@....net>,
        "tony.luck@...el.com" <tony.luck@...el.com>,
        "fenghua.yu@...el.com" <fenghua.yu@...el.com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "bp@...en8.de" <bp@...en8.de>, "hpa@...or.com" <hpa@...or.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
        "linux-ia64@...r.kernel.org" <linux-ia64@...r.kernel.org>,
        "iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Suthikulpanit, Suravee" <Suravee.Suthikulpanit@....com>,
        Joerg Roedel <jroedel@...e.de>
Subject: Re: [PATCH 10/11] iommu: Disable passthrough mode when SME is active

On 8/19/19 8:22 AM, Joerg Roedel wrote:
> From: Joerg Roedel <jroedel@...e.de>
> 
> Using Passthrough mode when SME is active causes certain
> devices to use the SWIOTLB bounce buffer. The bounce buffer
> code has an upper limit of 256kb for the size of DMA
> allocations, which is too small for certain devices and
> causes them to fail.
> 
> With this patch we enable IOMMU by default when SME is
> active in the system, making the default configuration work
> for more systems than it does now.
> 
> Users that don't want IOMMUs to be enabled still can disable
> them with kernel parameters.
> 
> Signed-off-by: Joerg Roedel <jroedel@...e.de>

Reviewed-by: Tom Lendacky <thomas.lendacky@....com>
Tested-by: Tom Lendacky <thomas.lendacky@....com>

> ---
>  drivers/iommu/iommu.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/iommu/iommu.c b/drivers/iommu/iommu.c
> index 01759d4ac70b..ec18c9630e93 100644
> --- a/drivers/iommu/iommu.c
> +++ b/drivers/iommu/iommu.c
> @@ -119,6 +119,11 @@ static int __init iommu_subsys_init(void)
>  			iommu_set_default_passthrough(false);
>  		else
>  			iommu_set_default_translated(false);
> +
> +		if (iommu_default_passthrough() && sme_active()) {
> +			pr_info("SME detected - Disabling default IOMMU Passthrough\n");
> +			iommu_set_default_translated(false);
> +		}
>  	}
>  
>  	pr_info("Default domain type: %s %s\n",
>