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From: Ram Pai <linuxram@us.ibm.com>
To: Michael Ellerman <mpe@ellerman.id.au>
Cc: andmike@us.ibm.com, mst@redhat.com, aik@ozlabs.ru,
	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, linuxppc-dev@lists.ozlabs.org,
	hch@lst.de, bauerman@linux.ibm.com, david@gibson.dropbear.id.au
Subject: RE: [RFC v1 2/2] powerpc/pseries/iommu: Use dma_iommu_ops for Secure VMs aswell.
Date: Thu, 7 Nov 2019 21:49:22 -0800
Message-ID: <20191108054922.GH5201@oc0525413822.ibm.com> (raw)
In-Reply-To: <87k18c56ej.fsf@mpe.ellerman.id.au>

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


  reply index

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-11-04 21:28 [RFC v1 0/2] Enable IOMMU support for pseries Secure VMs Ram Pai
2019-11-04 21:28 ` [RFC v1 1/2] powerpc/pseries/iommu: Share the per-cpu TCE page with the hypervisor Ram Pai
2019-11-04 21:28   ` [RFC v1 2/2] powerpc/pseries/iommu: Use dma_iommu_ops for Secure VMs aswell Ram Pai
2019-11-07 10:26     ` Michael Ellerman
2019-11-08  5:49       ` Ram Pai [this message]
2019-11-06  1:58   ` [RFC v1 1/2] powerpc/pseries/iommu: Share the per-cpu TCE page with the hypervisor Alexey Kardashevskiy
2019-11-06 17:01     ` Ram Pai
2019-11-07  5:58       ` Alexey Kardashevskiy
2019-11-07 10:29   ` Michael Ellerman
2019-11-08  6:05     ` Ram Pai
2019-11-06  1:59 ` [RFC v1 0/2] Enable IOMMU support for pseries Secure VMs Alexey Kardashevskiy
2019-11-06 16:46   ` Ram Pai
2019-11-06 18:06   ` Michael S. Tsirkin
2019-11-06 18:52     ` Michael Roth
2019-11-06 22:22       ` Ram Pai
2019-11-07  6:01     ` Alexey Kardashevskiy

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