Subject: Re: [PATCH kernel 2/2] powerpc/powernv/ioda2: Delay PE disposal

From: David Gibson <[email-masked]>
Date: Thu, 14 Apr 2016 11:40:33 +1000

On Fri, Apr 08, 2016 at 04:36:44PM +1000, Alexey Kardashevskiy wrote:
> When SRIOV is disabled, the existing code presumes there is no
> virtual function (VF) in use and destroys all associated PEs.
> However it is possible to get into the situation when the user
> activated SRIOV disabling while a VF is still in use via VFIO.
> For example, unbinding a physical function (PF) while there is a guest
> running with a VF passed throuhgh via VFIO will trigger the bug.
> 
> This defines an IODA2-specific IOMMU group release() callback.
> This moves all the disposal code from pnv_ioda_release_vf_PE() to this
> new callback so the cleanup happens when the last user of an IOMMU
> group released the reference.
> 
> As pnv_pci_ioda2_release_dma_pe() was reduced to just calling
> iommu_group_put(), this merges pnv_pci_ioda2_release_dma_pe()
> into pnv_ioda_release_vf_PE().
> 
> Signed-off-by: Alexey Kardashevskiy <[email-masked]>
> ---
>  arch/powerpc/platforms/powernv/pci-ioda.c | 33 +++++++++++++------------------
>  1 file changed, 14 insertions(+), 19 deletions(-)
> 
> diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c
> index ce9f2bf..8108c54 100644
> --- a/arch/powerpc/platforms/powernv/pci-ioda.c
> +++ b/arch/powerpc/platforms/powernv/pci-ioda.c
> @@ -1333,27 +1333,25 @@ static void pnv_pci_ioda2_set_bypass(struct pnv_ioda_pe *pe, bool enable);
>  static void pnv_pci_ioda2_group_release(void *iommu_data)
>  {
>  	struct iommu_table_group *table_group = iommu_data;
> +	struct pnv_ioda_pe *pe = container_of(table_group,
> +			struct pnv_ioda_pe, table_group);
> +	struct pci_controller *hose = pci_bus_to_host(pe->parent_dev->bus);
> +	struct pnv_phb *phb = hose->private_data;
> +	struct iommu_table *tbl = pe->table_group.tables[0];
> +	int64_t rc;
>  
> -	table_group->group = NULL;
> -}
> -
> -static void pnv_pci_ioda2_release_dma_pe(struct pci_dev *dev, struct pnv_ioda_pe *pe)
> -{
> -	struct iommu_table    *tbl;
> -	int64_t               rc;
> -
> -	tbl = pe->table_group.tables[0];
>  	rc = pnv_pci_ioda2_unset_window(&pe->table_group, 0);

Is it safe to go manipulating the PE windows, etc. after SR-IOV is
disabled?

When SR-IOV is disabled, you need to immediately disable the VF (I'm
guessing that happens somewhere) and stop all access to the VF
"hardware".  Only the iommu group structure *has* to stick around
until the reference count drops to zero.  I think other structures and
hardware reconfiguration can be deferred or done immediately,
whichever is more convenient.

>  	if (rc)
>  		pe_warn(pe, "OPAL error %ld release DMA window\n", rc);
>  
>  	pnv_pci_ioda2_set_bypass(pe, false);
> -	if (pe->table_group.group) {
> -		iommu_group_put(pe->table_group.group);
> -		BUG_ON(pe->table_group.group);
> -	}
> +
> +	BUG_ON(!tbl);
>  	pnv_pci_ioda2_table_free_pages(tbl);
> -	iommu_free_table(tbl, of_node_full_name(dev->dev.of_node));
> +	iommu_free_table(tbl, of_node_full_name(pe->parent_dev->dev.of_node));
> +
> +	pnv_ioda_deconfigure_pe(phb, pe);
> +	pnv_ioda_free_pe(phb, pe->pe_number);
>  }
>  
>  static void pnv_ioda_release_vf_PE(struct pci_dev *pdev)
> @@ -1376,16 +1374,13 @@ static void pnv_ioda_release_vf_PE(struct pci_dev *pdev)
>  		if (pe->parent_dev != pdev)
>  			continue;
>  
> -		pnv_pci_ioda2_release_dma_pe(pdev, pe);
> -
>  		/* Remove from list */
>  		mutex_lock(&phb->ioda.pe_list_mutex);
>  		list_del(&pe->list);
>  		mutex_unlock(&phb->ioda.pe_list_mutex);
>  
> -		pnv_ioda_deconfigure_pe(phb, pe);
> -
> -		pnv_ioda_free_pe(phb, pe->pe_number);
> +		if (pe->table_group.group)
> +			iommu_group_put(pe->table_group.group);
>  	}
>  }
>  

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson