linux-kernel - Re: [PATCH] intel-iommu: Turn off translations at shutdown

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Message-ID: <f3d7138b-b254-3c6d-b865-d3b6889aa896@linux.intel.com>
Date:   Fri, 8 Nov 2019 11:06:08 +0800
From:   Lu Baolu <baolu.lu@...ux.intel.com>
To:     Deepa Dinamani <deepa.kernel@...il.com>, joro@...tes.org,
        linux-kernel@...r.kernel.org
Cc:     baolu.lu@...ux.intel.com, iommu@...ts.linux-foundation.org,
        dwmw2@...radead.org
Subject: Re: [PATCH] intel-iommu: Turn off translations at shutdown

Hi,

On 11/8/19 4:59 AM, Deepa Dinamani wrote:
> The intel-iommu driver assumes that the iommu state is
> cleaned up at the start of the new kernel.
> But, when we try to kexec boot something other than the
> Linux kernel, the cleanup cannot be relied upon.
> Hence, cleanup before we go down for reboot.
> 
> Keeping the cleanup at initialization also, in case BIOS
> leaves the IOMMU enabled.
> 
> I considered turning off iommu only during kexec reboot,
> but a clean shutdown seems always a good idea. But if
> someone wants to make it conditional, we can do that.
> 
> Tested that before, the info message
> 'DMAR: Translation was enabled for <iommu> but we are not in kdump mode'
> would be reported for each iommu. The message will not appear when the
> DMA-remapping is not enabled on entry to the kernel.
> 
> Signed-off-by: Deepa Dinamani <deepa.kernel@...il.com>
> ---
>   drivers/iommu/intel-iommu.c | 22 ++++++++++++++++++++++
>   1 file changed, 22 insertions(+)
> 
> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> index fe8097078669..f0636b263722 100644
> --- a/drivers/iommu/intel-iommu.c
> +++ b/drivers/iommu/intel-iommu.c
> @@ -4764,6 +4764,26 @@ static void intel_disable_iommus(void)
>   		iommu_disable_translation(iommu);
>   }
>   
> +static void intel_iommu_shutdown(void)
> +{
> +	struct dmar_drhd_unit *drhd;
> +	struct intel_iommu *iommu = NULL;
> +
> +	if (no_iommu || dmar_disabled)
> +		return;
> +
> +	down_write(&dmar_global_lock);
> +
> +	/* Disable PMRs explicitly here. */
> +	for_each_iommu(iommu, drhd)
> +		iommu_disable_protect_mem_regions(iommu);
> +
> +	/* Make sure the IOMMUs are switched off */
> +	intel_disable_iommus();
> +
> +	up_write(&dmar_global_lock);
> +}
> +
>   static inline struct intel_iommu *dev_to_intel_iommu(struct device *dev)
>   {
>   	struct iommu_device *iommu_dev = dev_to_iommu_device(dev);
> @@ -5013,6 +5033,8 @@ int __init intel_iommu_init(void)
>   	}
>   	up_write(&dmar_global_lock);
>   
> +	x86_platform.iommu_shutdown = intel_iommu_shutdown;

How about moving it to detect_intel_iommu() in drivers/iommu/dmar.c? And
make sure that it's included with CONFIG_X86_64.

Best regards,
baolu

> +
>   #if defined(CONFIG_X86) && defined(CONFIG_SWIOTLB)
>   	/*
>   	 * If the system has no untrusted device or the user has decided
>