linux-kernel - Re: [PATCH v5 2/2] powerpc/pseries/iommu: Use dma_iommu

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Date:   Tue, 10 Dec 2019 14:08:52 +1100
From:   Alexey Kardashevskiy <aik@...abs.ru>
To:     Ram Pai <linuxram@...ibm.com>, mpe@...erman.id.au
Cc:     linuxppc-dev@...ts.ozlabs.org, benh@...nel.crashing.org,
        david@...son.dropbear.id.au, paulus@...abs.org,
        mdroth@...ux.vnet.ibm.com, hch@....de, andmike@...ibm.com,
        sukadev@...ux.vnet.ibm.com, mst@...hat.com, ram.n.pai@...il.com,
        cai@....pw, tglx@...utronix.de, bauerman@...ux.ibm.com,
        linux-kernel@...r.kernel.org, leonardo@...ux.ibm.com
Subject: Re: [PATCH v5 2/2] powerpc/pseries/iommu: Use dma_iommu_ops for
 Secure VM.



On 07/12/2019 12:12, 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. Disabling dma_iommu_ops
> path for secure VMs, helped enable dma_direct path.  This enabled
> support for bounce-buffering through SWIOTLB.  However it fails to
> operate when IOMMU is enabled, since I/O pages are not TCE mapped.
> 
> Renable dma_iommu_ops path for pseries Secure VMs.  It handles all
> cases including, TCE mapping I/O pages, in the presence of a
> IOMMU.
> 
> Signed-off-by: Ram Pai <linuxram@...ibm.com>


Reviewed-by: Alexey Kardashevskiy <aik@...abs.ru>

Although I still do not totally understand the mechanics of this
(swiotlb on top of huge DDW at 0x800.0000.0000.0000), this change looks
reasonable anyway.



> ---
>  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 67b5009..4e27d66 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"
> @@ -1346,15 +1345,7 @@ 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