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Subject: Re: [PATCH v4 2/2] powerpc/pseries/iommu: Use dma_iommu_ops for
 Secure VMs aswell.
To:     Ram Pai <linuxram@us.ibm.com>, linuxppc-dev@lists.ozlabs.org,
        mpe@ellerman.id.au
Cc:     benh@kernel.crashing.org, david@gibson.dropbear.id.au,
        paulus@ozlabs.org, mdroth@linux.vnet.ibm.com, hch@lst.de,
        andmike@us.ibm.com, sukadev@linux.vnet.ibm.com, mst@redhat.com,
        ram.n.pai@gmail.com, cai@lca.pw, tglx@linutronix.de,
        bauerman@linux.ibm.com, linux-kernel@vger.kernel.org
References: <1575269124-17885-1-git-send-email-linuxram@us.ibm.com>
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From:   Alexey Kardashevskiy <aik@ozlabs.ru>
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Date:   Tue, 3 Dec 2019 11:58:18 +1100
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On 02/12/2019 17:45, Ram Pai wrote:
> Commit edea902c1c1e ("powerpc/pseries/iommu: Don't use dma_iommu_ops on
> 	       secure guests")
> disabled dma_iommu_ops path, for secure VMs. The rationale for disabling
> the dma_iommu_ops path, was to use the dma_direct path, since it had
> inbuilt support for bounce-buffering through SWIOTLB.
> 
> However dma_iommu_ops is functionally much richer. Depending on the
> capabilities of the platform, it can handle direct DMA; with or without
> bounce buffering, and it can handle indirect DMA. Hence its better to
> leverage the richer functionality supported by dma_iommu_ops.

What exactly do we leverage after applying this patch? afaict things are
going to work in exact same old way with this applied, no? Thanks,


> 
> Renable dma_iommu_ops path for pseries Secure VMs.
> 
> Signed-off-by: Ram Pai <linuxram@us.ibm.com>
> ---
>  arch/powerpc/platforms/pseries/iommu.c | 11 +----------
>  1 file changed, 1 insertion(+), 10 deletions(-)
> 
> diff --git a/arch/powerpc/platforms/pseries/iommu.c b/arch/powerpc/platforms/pseries/iommu.c
> index 0720831..6adf4d3 100644
> --- a/arch/powerpc/platforms/pseries/iommu.c
> +++ b/arch/powerpc/platforms/pseries/iommu.c
> @@ -36,7 +36,6 @@
>  #include <asm/udbg.h>
>  #include <asm/mmzone.h>
>  #include <asm/plpar_wrappers.h>
> -#include <asm/svm.h>
>  #include <asm/ultravisor.h>
>  
>  #include "pseries.h"
> @@ -1337,15 +1336,7 @@ 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.
> -	 */
> -	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)
> 

-- 
Alexey