Subject: Re: [PATCH kernel v8 14/31] vfio: powerpc/spapr: powerpc/powernv/ioda2: Rework IOMMU ownership control

From: David Gibson <[email-masked]>
Date: Mon, 20 Apr 2015 12:44:46 +1000

On Fri, Apr 17, 2015 at 08:09:29PM +1000, Alexey Kardashevskiy wrote:
> On 04/16/2015 04:07 PM, David Gibson wrote:
> >On Fri, Apr 10, 2015 at 04:30:56PM +1000, Alexey Kardashevskiy wrote:
> >>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 a set_ownership() callback to it which is called when an external
> >>user takes control over the IOMMU.
> >
> >Do you really need separate ops structures at both the single table
> >and table group level?  The different tables in a group will all
> >belong to the same basic iommu won't they?
> 
> 
> IOMMU tables exist alone in VIO. Also, the platform code uses just a table
> (or it is in bypass mode) and does not care about table groups. It looked
> more clean for myself to keep them separated. Should I still merge
> those?

Ok, that sounds like a reasonable argument for keeping them separate,
at least for now.

> >>This renames set_bypass() to set_ownership() as it is not necessarily
> >>just enabling bypassing, it can be something else/more so let's give it
> >>more generic name. The bool parameter is inverted.
> >>
> >>The callback is implemented for IODA2 only. Other platforms (P5IOC2,
> >>IODA1) will use the old iommu_take_ownership/iommu_release_ownership API.
> >>
> >>Signed-off-by: Alexey Kardashevskiy <[email-masked]>
> >>---
> >>  arch/powerpc/include/asm/iommu.h          | 14 +++++++++++++-
> >>  arch/powerpc/platforms/powernv/pci-ioda.c | 30 ++++++++++++++++++++++--------
> >>  drivers/vfio/vfio_iommu_spapr_tce.c       | 25 +++++++++++++++++++++----
> >>  3 files changed, 56 insertions(+), 13 deletions(-)
> >>
> >>diff --git a/arch/powerpc/include/asm/iommu.h b/arch/powerpc/include/asm/iommu.h
> >>index b9e50d3..d1f8c6c 100644
> >>--- a/arch/powerpc/include/asm/iommu.h
> >>+++ b/arch/powerpc/include/asm/iommu.h
> >>@@ -92,7 +92,6 @@ struct iommu_table {
> >>  	unsigned long  it_page_shift;/* table iommu page size */
> >>  	struct iommu_table_group *it_group;
> >>  	struct iommu_table_ops *it_ops;
> >>-	void (*set_bypass)(struct iommu_table *tbl, bool enable);
> >>  };
> >>
> >>  /* Pure 2^n version of get_order */
> >>@@ -127,11 +126,24 @@ 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 enabled, the kernel cannot use IOMMU
> >>+	 * for itself.
> >>+	 */
> >>+	void (*set_ownership)(struct iommu_table_group *table_group,
> >>+			bool enable);
> >
> >The meaning of "enable" in a function called "set_ownership" is
> >entirely obscure.
> 
> Suggest something better please :) I have nothing better...

Well, given it's "set_ownershuip" you could have "owner" - that would
want to be an enum with OWNER_KERNEL and OWNER_VFIO or something
rather than a bool.

Or you could leave it a bool but call it "allow_bypass".

> 
> 
> >
> >>+};
> >>+
> >>  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/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c
> >>index a964c50..9687731 100644
> >>--- a/arch/powerpc/platforms/powernv/pci-ioda.c
> >>+++ b/arch/powerpc/platforms/powernv/pci-ioda.c
> >>@@ -1255,10 +1255,8 @@ 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_group, struct pnv_ioda_pe,
> >>-					      table_group);
> >>  	uint16_t window_id = (pe->pe_number << 1 ) + 1;
> >>  	int64_t rc;
> >>
> >>@@ -1286,7 +1284,8 @@ 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);
> >>  	}
> >>@@ -1302,13 +1301,27 @@ 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);
> >>  }
> >>
> >>+static void pnv_ioda2_set_ownership(struct iommu_table_group *table_group,
> >>+				     bool enable)
> >>+{
> >>+	struct pnv_ioda_pe *pe = container_of(table_group, struct pnv_ioda_pe,
> >>+						table_group);
> >>+	if (enable)
> >>+		iommu_take_ownership(table_group);
> >>+	else
> >>+		iommu_release_ownership(table_group);
> >>+
> >>+	pnv_pci_ioda2_set_bypass(pe, !enable);
> >>+}
> >>+
> >>+static struct iommu_table_group_ops pnv_pci_ioda2_ops = {
> >>+	.set_ownership = pnv_ioda2_set_ownership,
> >>+};
> >>+
> >>  static void pnv_pci_ioda2_setup_dma_pe(struct pnv_phb *phb,
> >>  				       struct pnv_ioda_pe *pe)
> >>  {
> >>@@ -1376,6 +1389,7 @@ static void pnv_pci_ioda2_setup_dma_pe(struct pnv_phb *phb,
> >>  	}
> >>  	tbl->it_ops = &pnv_iommu_ops;
> >>  	iommu_init_table(tbl, phb->hose->node);
> >>+	pe->table_group.ops = &pnv_pci_ioda2_ops;
> >>  	iommu_register_group(&pe->table_group, phb->hose->global_number,
> >>  			pe->pe_number);
> >>
> >>diff --git a/drivers/vfio/vfio_iommu_spapr_tce.c b/drivers/vfio/vfio_iommu_spapr_tce.c
> >>index 9f38351..d5d8c50 100644
> >>--- a/drivers/vfio/vfio_iommu_spapr_tce.c
> >>+++ b/drivers/vfio/vfio_iommu_spapr_tce.c
> >>@@ -535,9 +535,22 @@ static int tce_iommu_attach_group(void *iommu_data,
> >>  		goto unlock_exit;
> >>  	}
> >>
> >>-	ret = iommu_take_ownership(table_group);
> >>-	if (!ret)
> >>-		container->grp = iommu_group;
> >>+	if (!table_group->ops || !table_group->ops->set_ownership) {
> >>+		ret = iommu_take_ownership(table_group);
> >>+	} 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->set_ownership(table_group, true);
> >
> >And here to disable bypass you call it with enable=true, so it doesn't
> >even have the same meaning as it used to.
> 
> 
> I do not disable bypass per se (even if it what set_ownership(true) does) as
> it is IODA business and VFIO has no idea about it. I do take control over
> the group. I am not following you here - what used to have the same
> meaning?

Well, in set_bypass, the enable parameter was whether bypass was
enabled.  Here you're setting enable to true, when you want to
*disable* bypass (in the existing case).  If the "enable" parameter
isn't about enabling bypass, it's meaning is even more confusing than
I thought.

> >Plus, you should fold the logic to call the callback if necessary into
> >iommu_take_ownership().
> 
> 
> I really want to keep VFIO stuff out of arch/powerpc/kernel/iommu.c as much
> as possible as it is for platform DMA/IOMMU, not VFIO (which got SPAPR
> driver for that). ops->set_ownership() is one of these things.

What's VFIO specific about this fragment - it's just if you have the
callback, call it, otherwise fall back to the default.

> iommu_take_ownership()/iommu_release_ownership() are helpers for old-style
> commercially-unsupported P5IOC2/IODA1, and this is kind of a hack while
> ops->set_ownership() is an interface for VFIO to do dynamic windows thing.

Can you put their logic into a set_ownership callback for IODA1 then?

> If it makes sense, I could fold the previous patch into this one and move
> iommu_take_ownership()/iommu_release_ownership() to vfio_iommu_spapr_tce.c,
> should I? Or leave things are they are now.

That sounds like it might make sense.

> 
> 
> >>+		ret = 0;
> >>+	}
> >>+
> >>+	if (ret)
> >>+		goto unlock_exit;
> >>+
> >>+	container->grp = iommu_group;
> >>
> >>  unlock_exit:
> >>  	mutex_unlock(&container->lock);
> >>@@ -572,7 +585,11 @@ static void tce_iommu_detach_group(void *iommu_data,
> >>  	table_group = iommu_group_get_iommudata(iommu_group);
> >>  	BUG_ON(!table_group);
> >>
> >>-	iommu_release_ownership(table_group);
> >>+	/* Kernel owns the device now, we can restore bypass */
> >>+	if (!table_group->ops || !table_group->ops->set_ownership)
> >>+		iommu_release_ownership(table_group);
> >>+	else
> >>+		table_group->ops->set_ownership(table_group, false);
> >
> >Likewise fold this if into iommu_release_ownership().
> >
> >>  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