Subject: Re: [PATCH kernel v9 13/32] vfio: powerpc/spapr/iommu/powernv/ioda2: Rework IOMMU ownership control

From: David Gibson <[email-masked]>
Date: Wed, 29 Apr 2015 13:02:50 +1000

On Sat, Apr 25, 2015 at 10:14:37PM +1000, Alexey Kardashevskiy wrote:
> This adds tce_iommu_take_ownership() and tce_iommu_release_ownership
> which call in a loop iommu_take_ownership()/iommu_release_ownership()
> for every table on the group. As there is just one now, no change in
> behaviour is expected.
> 
> At the moment the iommu_table struct has a set_bypass() which enables/
> disables DMA bypass on IODA2 PHB. This is exposed to POWERPC IOMMU code
> which calls this callback when external IOMMU users such as VFIO are
> about to get over a PHB.
> 
> The set_bypass() callback is not really an iommu_table function but
> IOMMU/PE function. This introduces a iommu_table_group_ops struct and
> adds take_ownership()/release_ownership() callbacks to it which are
> called when an external user takes/releases control over the IOMMU.
> 
> This replaces set_bypass() with ownership callbacks as it is not
> necessarily just bypass enabling, it can be something else/more
> so let's give it more generic name.
> 
> The callbacks is implemented for IODA2 only. Other platforms (P5IOC2,
> IODA1) will use the old iommu_take_ownership/iommu_release_ownership API.
> The following patches will replace iommu_take_ownership/
> iommu_release_ownership calls in IODA2 with full IOMMU table release/
> create.
> 
> Signed-off-by: Alexey Kardashevskiy <[email-masked]>
> [aw: for the vfio related changes]
> Acked-by: Alex Williamson <[email-masked]>
> ---
> Changes:
> v9:
> * squashed "vfio: powerpc/spapr: powerpc/iommu: Rework IOMMU ownership control"
> and "vfio: powerpc/spapr: powerpc/powernv/ioda2: Rework IOMMU ownership control"
> into a single patch
> * moved helpers with a loop through tables in a group
> to vfio_iommu_spapr_tce.c to keep the platform code free of IOMMU table
> groups as much as possible
> * added missing tce_iommu_clear() to tce_iommu_release_ownership()
> * replaced the set_ownership(enable) callback with take_ownership() and
> release_ownership()
> ---
>  arch/powerpc/include/asm/iommu.h          | 13 +++++-
>  arch/powerpc/kernel/iommu.c               | 11 ------
>  arch/powerpc/platforms/powernv/pci-ioda.c | 40 +++++++++++++++----
>  drivers/vfio/vfio_iommu_spapr_tce.c       | 66 +++++++++++++++++++++++++++----
>  4 files changed, 103 insertions(+), 27 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/iommu.h b/arch/powerpc/include/asm/iommu.h
> index fa37519..e63419e 100644
> --- a/arch/powerpc/include/asm/iommu.h
> +++ b/arch/powerpc/include/asm/iommu.h
> @@ -93,7 +93,6 @@ struct iommu_table {
>  	unsigned long  it_page_shift;/* table iommu page size */
>  	struct iommu_table_group *it_table_group;
>  	struct iommu_table_ops *it_ops;
> -	void (*set_bypass)(struct iommu_table *tbl, bool enable);
>  };
>  
>  /* Pure 2^n version of get_order */
> @@ -128,11 +127,23 @@ extern struct iommu_table *iommu_init_table(struct iommu_table * tbl,
>  
>  #define IOMMU_TABLE_GROUP_MAX_TABLES	1
>  
> +struct iommu_table_group;
> +
> +struct iommu_table_group_ops {
> +	/*
> +	 * Switches ownership from the kernel itself to an external
> +	 * user. While onwership is taken, the kernel cannot use IOMMU itself.

Typo in "onwership".  I'd also like to see this be even more explicit
that "take" is the "core kernel -> vfio/whatever" transition and
release is the reverse.  

> +	 */
> +	void (*take_ownership)(struct iommu_table_group *table_group);
> +	void (*release_ownership)(struct iommu_table_group *table_group);
> +};
> +
>  struct iommu_table_group {
>  #ifdef CONFIG_IOMMU_API
>  	struct iommu_group *group;
>  #endif
>  	struct iommu_table tables[IOMMU_TABLE_GROUP_MAX_TABLES];
> +	struct iommu_table_group_ops *ops;
>  };
>  
>  #ifdef CONFIG_IOMMU_API
> diff --git a/arch/powerpc/kernel/iommu.c b/arch/powerpc/kernel/iommu.c
> index 005146b..2856d27 100644
> --- a/arch/powerpc/kernel/iommu.c
> +++ b/arch/powerpc/kernel/iommu.c
> @@ -1057,13 +1057,6 @@ int iommu_take_ownership(struct iommu_table *tbl)
>  
>  	memset(tbl->it_map, 0xff, sz);
>  
> -	/*
> -	 * Disable iommu bypass, otherwise the user can DMA to all of
> -	 * our physical memory via the bypass window instead of just
> -	 * the pages that has been explicitly mapped into the iommu
> -	 */
> -	if (tbl->set_bypass)
> -		tbl->set_bypass(tbl, false);
>  
>  	return 0;
>  }
> @@ -1078,10 +1071,6 @@ void iommu_release_ownership(struct iommu_table *tbl)
>  	/* Restore bit#0 set by iommu_init_table() */
>  	if (tbl->it_offset == 0)
>  		set_bit(0, tbl->it_map);
> -
> -	/* The kernel owns the device now, we can restore the iommu bypass */
> -	if (tbl->set_bypass)
> -		tbl->set_bypass(tbl, true);
>  }
>  EXPORT_SYMBOL_GPL(iommu_release_ownership);
>  
> diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c
> index 88472cb..718d5cc 100644
> --- a/arch/powerpc/platforms/powernv/pci-ioda.c
> +++ b/arch/powerpc/platforms/powernv/pci-ioda.c
> @@ -1870,10 +1870,8 @@ static void pnv_pci_ioda_setup_dma_pe(struct pnv_phb *phb,
>  		__free_pages(tce_mem, get_order(TCE32_TABLE_SIZE * segs));
>  }
>  
> -static void pnv_pci_ioda2_set_bypass(struct iommu_table *tbl, bool enable)
> +static void pnv_pci_ioda2_set_bypass(struct pnv_ioda_pe *pe, bool enable)
>  {
> -	struct pnv_ioda_pe *pe = container_of(tbl->it_table_group,
> -			struct pnv_ioda_pe, table_group);
>  	uint16_t window_id = (pe->pe_number << 1 ) + 1;
>  	int64_t rc;
>  
> @@ -1901,7 +1899,8 @@ static void pnv_pci_ioda2_set_bypass(struct iommu_table *tbl, bool enable)
>  		 * host side.
>  		 */
>  		if (pe->pdev)
> -			set_iommu_table_base(&pe->pdev->dev, tbl);
> +			set_iommu_table_base(&pe->pdev->dev,
> +					&pe->table_group.tables[0]);
>  		else
>  			pnv_ioda_setup_bus_dma(pe, pe->pbus, false);
>  	}
> @@ -1917,13 +1916,35 @@ static void pnv_pci_ioda2_setup_bypass_pe(struct pnv_phb *phb,
>  	/* TVE #1 is selected by PCI address bit 59 */
>  	pe->tce_bypass_base = 1ull << 59;
>  
> -	/* Install set_bypass callback for VFIO */
> -	pe->table_group.tables[0].set_bypass = pnv_pci_ioda2_set_bypass;
> -
>  	/* Enable bypass by default */
> -	pnv_pci_ioda2_set_bypass(&pe->table_group.tables[0], true);
> +	pnv_pci_ioda2_set_bypass(pe, true);
>  }
>  
> +#ifdef CONFIG_IOMMU_API
> +static void pnv_ioda2_take_ownership(struct iommu_table_group *table_group)
> +{
> +	struct pnv_ioda_pe *pe = container_of(table_group, struct pnv_ioda_pe,
> +						table_group);
> +
> +	iommu_take_ownership(&table_group->tables[0]);
> +	pnv_pci_ioda2_set_bypass(pe, false);
> +}
> +
> +static void pnv_ioda2_release_ownership(struct iommu_table_group *table_group)
> +{
> +	struct pnv_ioda_pe *pe = container_of(table_group, struct pnv_ioda_pe,
> +						table_group);
> +
> +	iommu_release_ownership(&table_group->tables[0]);
> +	pnv_pci_ioda2_set_bypass(pe, true);
> +}
> +
> +static struct iommu_table_group_ops pnv_pci_ioda2_ops = {
> +	.take_ownership = pnv_ioda2_take_ownership,
> +	.release_ownership = pnv_ioda2_release_ownership,
> +};
> +#endif
> +
>  static void pnv_pci_ioda2_setup_dma_pe(struct pnv_phb *phb,
>  				       struct pnv_ioda_pe *pe)
>  {
> @@ -1991,6 +2012,9 @@ static void pnv_pci_ioda2_setup_dma_pe(struct pnv_phb *phb,
>  	}
>  	tbl->it_ops = &pnv_ioda2_iommu_ops;
>  	iommu_init_table(tbl, phb->hose->node);
> +#ifdef CONFIG_IOMMU_API
> +	pe->table_group.ops = &pnv_pci_ioda2_ops;
> +#endif
>  
>  	if (pe->flags & PNV_IODA_PE_DEV) {
>  		iommu_register_group(&pe->table_group, phb->hose->global_number,
> diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
> index 17e884a..dacc738 100644
> --- a/drivers/vfio/vfio_iommu_spapr_tce.c
> +++ b/drivers/vfio/vfio_iommu_spapr_tce.c
> @@ -483,6 +483,43 @@ static long tce_iommu_ioctl(void *iommu_data,
>  	return -ENOTTY;
>  }
>  
> +static void tce_iommu_release_ownership(struct tce_container *container,
> +		struct iommu_table_group *table_group)
> +{
> +	int i;
> +
> +	for (i = 0; i < IOMMU_TABLE_GROUP_MAX_TABLES; ++i) {
> +		struct iommu_table *tbl = &table_group->tables[i];
> +
> +		tce_iommu_clear(container, tbl, tbl->it_offset, tbl->it_size);
> +		if (tbl->it_map)
> +			iommu_release_ownership(tbl);
> +	}
> +}
> +
> +static int tce_iommu_take_ownership(struct iommu_table_group *table_group)
> +{
> +	int i, j, rc = 0;
> +
> +	for (i = 0; i < IOMMU_TABLE_GROUP_MAX_TABLES; ++i) {
> +		struct iommu_table *tbl = &table_group->tables[i];
> +
> +		if (!tbl->it_map)
> +			continue;
> +
> +		rc = iommu_take_ownership(tbl);
> +		if (rc) {
> +			for (j = 0; j < i; ++j)
> +				iommu_release_ownership(
> +						&table_group->tables[j]);
> +
> +			return rc;
> +		}
> +	}
> +
> +	return 0;
> +}
> +
>  static int tce_iommu_attach_group(void *iommu_data,
>  		struct iommu_group *iommu_group)
>  {
> @@ -515,9 +552,23 @@ static int tce_iommu_attach_group(void *iommu_data,
>  		goto unlock_exit;
>  	}
>  
> -	ret = iommu_take_ownership(&table_group->tables[0]);
> -	if (!ret)
> -		container->grp = iommu_group;
> +	if (!table_group->ops || !table_group->ops->take_ownership ||
> +			!table_group->ops->release_ownership) {
> +		ret = tce_iommu_take_ownership(table_group);

Haven't looked at the rest of the series.  I'm hoping that you're
eventually planning to replace this fallback with setting the
take_ownership call for p5ioc etc. to point to
tce_iommu_take_ownership.

> +	} else {
> +		/*
> +		 * Disable iommu bypass, otherwise the user can DMA to all of
> +		 * our physical memory via the bypass window instead of just
> +		 * the pages that has been explicitly mapped into the iommu
> +		 */
> +		table_group->ops->take_ownership(table_group);
> +		ret = 0;
> +	}
> +
> +	if (ret)
> +		goto unlock_exit;
> +
> +	container->grp = iommu_group;
>  
>  unlock_exit:
>  	mutex_unlock(&container->lock);
> @@ -530,7 +581,6 @@ static void tce_iommu_detach_group(void *iommu_data,
>  {
>  	struct tce_container *container = iommu_data;
>  	struct iommu_table_group *table_group;
> -	struct iommu_table *tbl;
>  
>  	mutex_lock(&container->lock);
>  	if (iommu_group != container->grp) {
> @@ -553,9 +603,11 @@ static void tce_iommu_detach_group(void *iommu_data,
>  	table_group = iommu_group_get_iommudata(iommu_group);
>  	BUG_ON(!table_group);
>  
> -	tbl = &table_group->tables[0];
> -	tce_iommu_clear(container, tbl, tbl->it_offset, tbl->it_size);
> -	iommu_release_ownership(tbl);
> +	/* Kernel owns the device now, we can restore bypass */
> +	if (!table_group->ops || !table_group->ops->release_ownership)
> +		tce_iommu_release_ownership(container, table_group);
> +	else
> +		table_group->ops->release_ownership(table_group);
>  
>  unlock_exit:
>  	mutex_unlock(&container->lock);

-- 
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