Re: [PATCH] iommu/vt-d: Make sure IOMMUs are off when intel_iommu=off

[Jacob Pan <jacob.jun.pan@linux.intel.com>]

On Wed, 29 Mar 2017 17:00:39 +0200
Joerg Roedel <joro@8bytes.org> wrote:

> From: Joerg Roedel <jroedel@suse.de>
> 
> When booting into a kexec kernel with intel_iommu=off, and
> the previous kernel had intel_iommu=on, the IOMMU hardware
> is still enabled and gets not disabled by the new kernel.
> 
> This causes the boot to fail because DMA is blocked by the
> hardware. Disable the IOMMUs when we find it enabled in the
> kexec kernel and boot with intel_iommu=off.
> 
> Signed-off-by: Joerg Roedel <jroedel@suse.de>
> ---
>  drivers/iommu/intel-iommu.c | 18 +++++++++++++++++-
>  1 file changed, 17 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/intel-iommu.c b/drivers/iommu/intel-iommu.c
> index d412a31..1662288 100644
> --- a/drivers/iommu/intel-iommu.c
> +++ b/drivers/iommu/intel-iommu.c
> @@ -4730,6 +4730,15 @@ static int intel_iommu_cpu_dead(unsigned int
> cpu) return 0;
>  }
>  
> +static void intel_disable_iommus(void)
> +{
> +	struct intel_iommu *iommu = NULL;
> +	struct dmar_drhd_unit *drhd;
> +
> +	for_each_iommu(iommu, drhd)
> +		iommu_disable_translation(iommu);
should we also disable IR here? i.e.
iommu_disable_irq_remapping(iommu);

> +}
> +
>  static inline struct intel_iommu *dev_to_intel_iommu(struct device
> *dev) {
>  	return container_of(dev, struct intel_iommu, iommu.dev);
> @@ -4840,8 +4849,15 @@ int __init intel_iommu_init(void)
>  		goto out_free_dmar;
>  	}
>  
> -	if (no_iommu || dmar_disabled)
> +	if (no_iommu || dmar_disabled) {
> +		/*
> +		 * Make sure the IOMMUs are switched off, even when
> we
> +		 * boot into a kexec kernel and the previous kernel
> left
> +		 * them enabled
> +		 */
> +		intel_disable_iommus();
>  		goto out_free_dmar;
> +	}
>  
>  	if (list_empty(&dmar_rmrr_units))
>  		pr_info("No RMRR found\n");

[Jacob Pan]