Re: [PATCH v5 2/2] powerpc/pseries/iommu: Use dma_iommu_ops for Secure VM.

Alexey Kardashevskiy
2019-12-10T03:09:03Z

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@us.ibm.com>

Reviewed-by: Alexey Kardashevskiy <aik@ozlabs.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