linux-kernel - Re: [RFC v1 2/2] powerpc/pseries/iommu: Use dma_iommu

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Message-ID: <87k18c56ej.fsf@mpe.ellerman.id.au>
Date:   Thu, 07 Nov 2019 21:26:28 +1100
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Ram Pai <linuxram@...ibm.com>, linuxppc-dev@...ts.ozlabs.org
Cc:     benh@...nel.crashing.org, david@...son.dropbear.id.au,
        paulus@...abs.org, mdroth@...ux.vnet.ibm.com, hch@....de,
        linuxram@...ibm.com, andmike@...ibm.com,
        sukadev@...ux.vnet.ibm.com, mst@...hat.com, ram.n.pai@...il.com,
        aik@...abs.ru, cai@....pw, tglx@...utronix.de,
        bauerman@...ux.ibm.com, linux-kernel@...r.kernel.org
Subject: Re: [RFC v1 2/2] powerpc/pseries/iommu: Use dma_iommu_ops for Secure VMs aswell.

Ram Pai <linuxram@...ibm.com> writes:
> This enables IOMMU support for pseries Secure VMs.

Can you give us some more explanation please?

This is basically a revert of commit:
  edea902c1c1e ("powerpc/pseries/iommu: Don't use dma_iommu_ops on secure guests")

But neglects to remove the now unnecessary include of svm.h.

> diff --git a/arch/powerpc/platforms/pseries/iommu.c b/arch/powerpc/platforms/pseries/iommu.c
> index 07f0847..189717b 100644
> --- a/arch/powerpc/platforms/pseries/iommu.c
> +++ b/arch/powerpc/platforms/pseries/iommu.c
> @@ -1333,15 +1333,7 @@ void iommu_init_early_pSeries(void)
>  	of_reconfig_notifier_register(&iommu_reconfig_nb);
>  	register_memory_notifier(&iommu_mem_nb);
>  
> -	/*
> -	 * Secure guest memory is inacessible to devices so regular DMA isn't
> -	 * possible.
> -	 *
> -	 * In that case keep devices' dma_map_ops as NULL so that the generic
> -	 * DMA code path will use SWIOTLB to bounce buffers for DMA.

Please explain what has changed to make this no longer necessary.

cheers

> -	 */
> -	if (!is_secure_guest())
> -		set_pci_dma_ops(&dma_iommu_ops);
> +	set_pci_dma_ops(&dma_iommu_ops);
>  }
>  
>  static int __init disable_multitce(char *str)
> -- 
> 1.8.3.1