Re: [PATCH] iommu/amd: Do not disable SWIOTLB if SME is active

[Tom Lendacky <thomas.lendacky-5C7GfCeVMHo@public.gmane.org>]

On 10/6/2017 4:35 PM, Tom Lendacky wrote:
> When SME memory encryption is active it will rely on SWIOTLB to handle
> DMA for devices that cannot support the addressing requirements of
> having the encryption mask set in the physical address.  The IOMMU
> currently disables SWIOTLB if it is not running in passthrough mode.
> This is not desired as non-PCI devices attempting DMA may fail. Update
> the code to check if SME is active and not disable SWIOTLB.
> 
> Signed-off-by: Tom Lendacky <thomas.lendacky-5C7GfCeVMHo@public.gmane.org>
> ---
>   drivers/iommu/amd_iommu.c |   10 ++++++----
>   1 file changed, 6 insertions(+), 4 deletions(-)
> 

Hi Joerg,

This is an SME bug fix.  Assuming this is acceptable, any chance it can be
pushed to the current 4.14 linux rc release tree?

Thanks,
Tom

> diff --git a/drivers/iommu/amd_iommu.c b/drivers/iommu/amd_iommu.c
> index 51f8215..822679a 100644
> --- a/drivers/iommu/amd_iommu.c
> +++ b/drivers/iommu/amd_iommu.c
> @@ -2773,14 +2773,16 @@ int __init amd_iommu_init_api(void)
>   
>   int __init amd_iommu_init_dma_ops(void)
>   {
> -	swiotlb        = iommu_pass_through ? 1 : 0;
> +	swiotlb        = (iommu_pass_through || sme_me_mask) ? 1 : 0;
>   	iommu_detected = 1;
>   
>   	/*
>   	 * In case we don't initialize SWIOTLB (actually the common case
> -	 * when AMD IOMMU is enabled), make sure there are global
> -	 * dma_ops set as a fall-back for devices not handled by this
> -	 * driver (for example non-PCI devices).
> +	 * when AMD IOMMU is enabled and SME is not active), make sure there
> +	 * are global dma_ops set as a fall-back for devices not handled by
> +	 * this driver (for example non-PCI devices). When SME is active,
> +	 * make sure that swiotlb variable remains set so the global dma_ops
> +	 * continue to be SWIOTLB.
>   	 */
>   	if (!swiotlb)
>   		dma_ops = &nommu_dma_ops;
>