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From: Alexey Kardashevskiy <aik@ozlabs.ru>
To: Ram Pai <linuxram@us.ibm.com>,
	linuxppc-dev@lists.ozlabs.org, mpe@ellerman.id.au
Cc: andmike@us.ibm.com, mst@redhat.com, mdroth@linux.vnet.ibm.com,
	linux-kernel@vger.kernel.org, ram.n.pai@gmail.com, cai@lca.pw,
	tglx@linutronix.de, sukadev@linux.vnet.ibm.com, hch@lst.de,
	bauerman@linux.ibm.com, david@gibson.dropbear.id.au
Subject: Re: [PATCH v4 2/2] powerpc/pseries/iommu: Use dma_iommu_ops for Secure VMs aswell.
Date: Tue, 3 Dec 2019 11:58:18 +1100
Message-ID: <58b08d09-aaf8-5659-c4e8-c502c508f35c@ozlabs.ru> (raw)
In-Reply-To: <1575269124-17885-3-git-send-email-linuxram@us.ibm.com>



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

  reply index

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-12-02  6:45 [PATCH v4 0/2] Enable IOMMU support for pseries Secure VMs Ram Pai
2019-12-02  6:45 ` [PATCH v4 1/2] powerpc/pseries/iommu: Share the per-cpu TCE page with the hypervisor Ram Pai
2019-12-02  6:45   ` [PATCH v4 2/2] powerpc/pseries/iommu: Use dma_iommu_ops for Secure VMs aswell Ram Pai
2019-12-03  0:58     ` Alexey Kardashevskiy [this message]
2019-12-03  4:07       ` Ram Pai
2019-12-03  0:56   ` [PATCH v4 1/2] powerpc/pseries/iommu: Share the per-cpu TCE page with the hypervisor Alexey Kardashevskiy
2019-12-03  2:08     ` Ram Pai
2019-12-03  2:15       ` Alexey Kardashevskiy
2019-12-03  4:05         ` Ram Pai
2019-12-03  4:24           ` Alexey Kardashevskiy
2019-12-03 16:52             ` Ram Pai
2019-12-04  0:04               ` Alexey Kardashevskiy
2019-12-04  0:49                 ` Ram Pai
2019-12-04  1:08                   ` Alexey Kardashevskiy
2019-12-04  3:36                     ` David Gibson
2019-12-04 20:42                       ` Ram Pai
2019-12-04 22:26                         ` Alexey Kardashevskiy
2019-12-05  2:15                           ` [PATCH v4 1/2] powerpc/pseries/iommu: Share the per-cpu TCE page with the hypervisor.y Ram Pai
2019-12-06 23:10                           ` [PATCH v4 1/2] powerpc/pseries/iommu: Share the per-cpu TCE page with the hypervisor Ram Pai
2019-12-05  8:28                         ` Christoph Hellwig
2019-12-04 18:26   ` Leonardo Bras
2019-12-04 20:27     ` Ram Pai

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