Subject: Re: [PATCH kernel v9 23/32] powerpc/powernv/ioda: Define and implement DMA table/window management callbacks

From: David Gibson <[email-masked]>
Date: Fri, 1 May 2015 13:36:58 +1000

On Thu, Apr 30, 2015 at 07:56:17PM +1000, Alexey Kardashevskiy wrote:
> On 04/30/2015 02:37 PM, David Gibson wrote:
> >On Wed, Apr 29, 2015 at 07:44:20PM +1000, Alexey Kardashevskiy wrote:
> >>On 04/29/2015 03:30 PM, David Gibson wrote:
> >>>On Sat, Apr 25, 2015 at 10:14:47PM +1000, Alexey Kardashevskiy wrote:
> >>>>This extends iommu_table_group_ops by a set of callbacks to support
> >>>>dynamic DMA windows management.
> >>>>
> >>>>create_table() creates a TCE table with specific parameters.
> >>>>it receives iommu_table_group to know nodeid in order to allocate
> >>>>TCE table memory closer to the PHB. The exact format of allocated
> >>>>multi-level table might be also specific to the PHB model (not
> >>>>the case now though).
> >>>>This callback calculated the DMA window offset on a PCI bus from @num
> >>>>and stores it in a just created table.
> >>>>
> >>>>set_window() sets the window at specified TVT index + @num on PHB.
> >>>>
> >>>>unset_window() unsets the window from specified TVT.
> >>>>
> >>>>This adds a free() callback to iommu_table_ops to free the memory
> >>>>(potentially a tree of tables) allocated for the TCE table.
> >>>
> >>>Doesn't the free callback belong with the previous patch introducing
> >>>multi-level tables?
> >>
> >>
> >>
> >>If I did that, you would say "why is it here if nothing calls it" on
> >>"multilevel" patch and "I see the allocation but I do not see memory
> >>release" ;)
> >
> >Yeah, fair enough ;)
> >
> >>I need some rule of thumb here. I think it is a bit cleaner if the same
> >>patch adds a callback for memory allocation and its counterpart, no?
> >
> >On further consideration, yes, I think you're right.
> >
> >>>>create_table() and free() are supposed to be called once per
> >>>>VFIO container and set_window()/unset_window() are supposed to be
> >>>>called for every group in a container.
> >>>>
> >>>>This adds IOMMU capabilities to iommu_table_group such as default
> >>>>32bit window parameters and others.
> >>>>
> >>>>Signed-off-by: Alexey Kardashevskiy <[email-masked]>
> >>>>---
> >>>>  arch/powerpc/include/asm/iommu.h            | 19 ++++++++
> >>>>  arch/powerpc/platforms/powernv/pci-ioda.c   | 75 ++++++++++++++++++++++++++---
> >>>>  arch/powerpc/platforms/powernv/pci-p5ioc2.c | 12 +++--
> >>>>  3 files changed, 96 insertions(+), 10 deletions(-)
> >>>>
> >>>>diff --git a/arch/powerpc/include/asm/iommu.h b/arch/powerpc/include/asm/iommu.h
> >>>>index 0f50ee2..7694546 100644
> >>>>--- a/arch/powerpc/include/asm/iommu.h
> >>>>+++ b/arch/powerpc/include/asm/iommu.h
> >>>>@@ -70,6 +70,7 @@ struct iommu_table_ops {
> >>>>  	/* get() returns a physical address */
> >>>>  	unsigned long (*get)(struct iommu_table *tbl, long index);
> >>>>  	void (*flush)(struct iommu_table *tbl);
> >>>>+	void (*free)(struct iommu_table *tbl);
> >>>>  };
> >>>>
> >>>>  /* These are used by VIO */
> >>>>@@ -148,6 +149,17 @@ extern struct iommu_table *iommu_init_table(struct iommu_table * tbl,
> >>>>  struct iommu_table_group;
> >>>>
> >>>>  struct iommu_table_group_ops {
> >>>>+	long (*create_table)(struct iommu_table_group *table_group,
> >>>>+			int num,
> >>>>+			__u32 page_shift,
> >>>>+			__u64 window_size,
> >>>>+			__u32 levels,
> >>>>+			struct iommu_table *tbl);
> >>>>+	long (*set_window)(struct iommu_table_group *table_group,
> >>>>+			int num,
> >>>>+			struct iommu_table *tblnew);
> >>>>+	long (*unset_window)(struct iommu_table_group *table_group,
> >>>>+			int num);
> >>>>  	/*
> >>>>  	 * Switches ownership from the kernel itself to an external
> >>>>  	 * user. While onwership is taken, the kernel cannot use IOMMU itself.
> >>>>@@ -160,6 +172,13 @@ struct iommu_table_group {
> >>>>  #ifdef CONFIG_IOMMU_API
> >>>>  	struct iommu_group *group;
> >>>>  #endif
> >>>>+	/* Some key properties of IOMMU */
> >>>>+	__u32 tce32_start;
> >>>>+	__u32 tce32_size;
> >>>>+	__u64 pgsizes; /* Bitmap of supported page sizes */
> >>>>+	__u32 max_dynamic_windows_supported;
> >>>>+	__u32 max_levels;
> >>>
> >>>With this information, table_group seems even more like a bad name.
> >>>"iommu_state" maybe?
> >>
> >>
> >>Please, no. We will never come to agreement then :( And "iommu_state" is too
> >>general anyway, it won't pass.
> >>
> >>
> >>>>  	struct iommu_table tables[IOMMU_TABLE_GROUP_MAX_TABLES];
> >>>>  	struct iommu_table_group_ops *ops;
> >>>>  };
> >>>>diff --git a/arch/powerpc/platforms/powernv/pci-ioda.c b/arch/powerpc/platforms/powernv/pci-ioda.c
> >>>>index cc1d09c..4828837 100644
> >>>>--- a/arch/powerpc/platforms/powernv/pci-ioda.c
> >>>>+++ b/arch/powerpc/platforms/powernv/pci-ioda.c
> >>>>@@ -24,6 +24,7 @@
> >>>>  #include <linux/msi.h>
> >>>>  #include <linux/memblock.h>
> >>>>  #include <linux/iommu.h>
> >>>>+#include <linux/sizes.h>
> >>>>
> >>>>  #include <asm/sections.h>
> >>>>  #include <asm/io.h>
> >>>>@@ -1846,6 +1847,7 @@ static struct iommu_table_ops pnv_ioda2_iommu_ops = {
> >>>>  #endif
> >>>>  	.clear = pnv_ioda2_tce_free,
> >>>>  	.get = pnv_tce_get,
> >>>>+	.free = pnv_pci_free_table,
> >>>>  };
> >>>>
> >>>>  static void pnv_pci_ioda_setup_opal_tce_kill(struct pnv_phb *phb,
> >>>>@@ -1936,6 +1938,8 @@ static void pnv_pci_ioda_setup_dma_pe(struct pnv_phb *phb,
> >>>>  				 TCE_PCI_SWINV_PAIR);
> >>>>
> >>>>  	tbl->it_ops = &pnv_ioda1_iommu_ops;
> >>>>+	pe->table_group.tce32_start = tbl->it_offset << tbl->it_page_shift;
> >>>>+	pe->table_group.tce32_size = tbl->it_size << tbl->it_page_shift;
> >>>>  	iommu_init_table(tbl, phb->hose->node);
> >>>>
> >>>>  	if (pe->flags & PNV_IODA_PE_DEV) {
> >>>>@@ -1961,7 +1965,7 @@ static void pnv_pci_ioda_setup_dma_pe(struct pnv_phb *phb,
> >>>>  }
> >>>>
> >>>>  static long pnv_pci_ioda2_set_window(struct iommu_table_group *table_group,
> >>>>-		struct iommu_table *tbl)
> >>>>+		int num, struct iommu_table *tbl)
> >>>>  {
> >>>>  	struct pnv_ioda_pe *pe = container_of(table_group, struct pnv_ioda_pe,
> >>>>  			table_group);
> >>>>@@ -1972,9 +1976,10 @@ static long pnv_pci_ioda2_set_window(struct iommu_table_group *table_group,
> >>>>  	const __u64 start_addr = tbl->it_offset << tbl->it_page_shift;
> >>>>  	const __u64 win_size = tbl->it_size << tbl->it_page_shift;
> >>>>
> >>>>-	pe_info(pe, "Setting up window at %llx..%llx "
> >>>>+	pe_info(pe, "Setting up window#%d at %llx..%llx "
> >>>>  			"pgsize=0x%x tablesize=0x%lx "
> >>>>  			"levels=%d levelsize=%x\n",
> >>>>+			num,
> >>>>  			start_addr, start_addr + win_size - 1,
> >>>>  			1UL << tbl->it_page_shift, tbl->it_size << 3,
> >>>>  			tbl->it_indirect_levels + 1, tbl->it_level_size << 3);
> >>>>@@ -1987,7 +1992,7 @@ static long pnv_pci_ioda2_set_window(struct iommu_table_group *table_group,
> >>>>  	 */
> >>>>  	rc = opal_pci_map_pe_dma_window(phb->opal_id,
> >>>>  			pe->pe_number,
> >>>>-			pe->pe_number << 1,
> >>>>+			(pe->pe_number << 1) + num,
> >>>
> >>>Heh, yes, well, that makes it rather clear that only 2 tables are possible.
> >>>
> >>>>  			tbl->it_indirect_levels + 1,
> >>>>  			__pa(tbl->it_base),
> >>>>  			size << 3,
> >>>>@@ -2000,7 +2005,7 @@ static long pnv_pci_ioda2_set_window(struct iommu_table_group *table_group,
> >>>>  	pnv_pci_ioda2_tvt_invalidate(pe);
> >>>>
> >>>>  	/* Store fully initialized *tbl (may be external) in PE */
> >>>>-	pe->table_group.tables[0] = *tbl;
> >>>>+	pe->table_group.tables[num] = *tbl;
> >>>
> >>>I'm a bit confused by this whole set_window thing.  Is the idea that
> >>>with multiple groups in a container you have multiple table_group s
> >>>each with different copies of the iommu_table structures, but pointing
> >>>to the same actual TCE entries (it_base)?
> >>
> >>Yes.
> >>
> >>>It seems to me not terribly
> >>>obvious when you "create" a table and when you "set" a window.
> >>
> >>
> >>A table is not attached anywhere until its address is programmed (in
> >>set_window()) to the hardware, it is just a table in memory. For
> >>POWER8/IODA2, I create a table before I attach any group to a container,
> >>then I program this table to every attached container, right now it is done
> >>in container's attach_group(). So later we can hotplug any host PCI device
> >>to a container - it will program same TCE table to every new group in the
> >>container.
> >
> >So you "create" once, then "set" it to one or more table_groups?  It
> >seems odd that "create" is a table_group callback in that case.
> 
> 
> Where else could it be? ppc_md? We are getting rid of these. Some global
> function? We do not want VFIO to know about this. I run out of ideas here.

Yeah, I guess it has to be in table_group, despite the oddness.  I
guess the point is that it's the first group that determines the type
of IOMMU you're using for this container.  IIRC you already check on
set_window that any additional groups have a compatible
(i.e. identical) IOMMU.

-- 
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