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SubjectRE: [RFC v1 2/2] powerpc/pseries/iommu: Use dma_iommu_ops for Secure VMs aswell.
On Thu, Nov 07, 2019 at 09:26:28PM +1100, Michael Ellerman wrote:
> Ram Pai <linuxram@us.ibm.com> writes:
> > This enables IOMMU support for pseries Secure VMs.
>
> Can you give us some more explanation please?

Yes. Will do.

The simple explanation is -- it was a mistake. We should
not have disabled IOMMU ops for secure guests. Though it enabled
us to use virtio devices, with the help of some additional patches to
the virtio subsystem; in hindsight, we should not have disabled IOMMU
ops for secure VMs :-(.

RP



>
> 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

--
Ram Pai

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