linux-kernel - Re: [kernel, v12, 17/34] powerpc/spapr: vfio: Switch from iommu_table to new iommu_table

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Date:	Wed, 10 Jun 2015 17:33:07 +1000 (AEST)
From:	Michael Ellerman <mpe@...erman.id.au>
To:	Alexey Kardashevskiy <aik@...abs.ru>, linuxppc-dev@...ts.ozlabs.org
Cc:	Wei Yang <weiyang@...ux.vnet.ibm.com>,
	Alexey Kardashevskiy <aik@...abs.ru>,
	Gavin Shan <gwshan@...ux.vnet.ibm.com>,
	linux-kernel@...r.kernel.org,
	Alex Williamson <alex.williamson@...hat.com>,
	Paul Mackerras <paulus@...ba.org>,
	David Gibson <david@...son.dropbear.id.au>
Subject: Re: [kernel, v12, 17/34] powerpc/spapr: vfio: Switch from iommu_table to new iommu_table_group

On Fri, 2015-05-06 at 06:35:09 UTC, Alexey Kardashevskiy wrote:
> So far one TCE table could only be used by one IOMMU group. However
> IODA2 hardware allows programming the same TCE table address to
> multiple PE allowing sharing tables.

...

> +	pnv_pci_link_table_and_group(phb->hose->node, 0, tbl, &pe->table_group);
> +	pnv_pci_link_table_and_group(phb->hose->node, 0, tbl, &pe->table_group);
> +		pnv_pci_link_table_and_group(phb->hose->node, 0,
> +				tbl, &phb->p5ioc2.table_group);

> +long pnv_pci_link_table_and_group(int node, int num,
> +		struct iommu_table *tbl,
> +		struct iommu_table_group *table_group)
> +{
> +	struct iommu_table_group_link *tgl = NULL;
> +
> +	BUG_ON(!tbl);
> +	BUG_ON(!table_group);
> +	BUG_ON(!table_group->group);
> +
> +	tgl = kzalloc_node(sizeof(struct iommu_table_group_link), GFP_KERNEL,
> +			node);
> +	if (!tgl)
> +		return -ENOMEM;
> +
> +	tgl->table_group = table_group;
> +	list_add_rcu(&tgl->next, &tbl->it_group_list);
> +
> +	table_group->tables[num] = tbl;
> +
> +	return 0;

I'm not a fan of the BUG_ONs here.

This routine is so important that you have to BUG_ON three times at the start,
yet you never check the return code if it fails? That doesn't make sense to me.

If anything this should be sufficient:

	if (WARN_ON(!tbl || !table_group))
		return -EINVAL;

cheers
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