Re: [PATCH v4 10/11] powerpc/pseries/iommu: Make use of DDW for indirect mapping

[Leonardo Brás]

On Tue, 2021-05-11 at 17:57 +1000, Alexey Kardashevskiy wrote:
> 
> 
> On 01/05/2021 02:31, Leonardo Bras wrote:
> > [...]
> >       pmem_present = dn != NULL;
> > @@ -1218,8 +1224,12 @@ static bool enable_ddw(struct pci_dev *dev,
> > struct device_node *pdn)
> >   
> >         mutex_lock(&direct_window_init_mutex);
> >   
> > -       if (find_existing_ddw(pdn, &dev->dev.archdata.dma_offset,
> > &len))
> > -               goto out_unlock;
> > +       if (find_existing_ddw(pdn, &dev->dev.archdata.dma_offset,
> > &len)) {
> > +               direct_mapping = (len >= max_ram_len);
> > +
> > +               mutex_unlock(&direct_window_init_mutex);
> > +               return direct_mapping;
> 
> Does not this break the existing case when direct_mapping==true by 
> skipping setting dev->dev.bus_dma_limit before returning?
> 

Yes, it does. Good catch!
I changed it to use a flag instead of win64 for return, and now I can
use the same success exit path for both the new config and the config
found in list. (out_unlock)

> 
> 
> > +       }
> >   
> >         /*
> >          * If we already went through this for a previous function of
> > @@ -1298,7 +1308,6 @@ static bool enable_ddw(struct pci_dev *dev,
> > struct device_node *pdn)
> >                 goto out_failed;
> >         }
> >         /* verify the window * number of ptes will map the partition
> > */
> > -       /* check largest block * page size > max memory hotplug addr
> > */
> >         /*
> >          * The "ibm,pmemory" can appear anywhere in the address
> > space.
> >          * Assuming it is still backed by page structs, try
> > MAX_PHYSMEM_BITS
> > @@ -1320,6 +1329,17 @@ static bool enable_ddw(struct pci_dev *dev,
> > struct device_node *pdn)
> >                         1ULL << len,
> >                         query.largest_available_block,
> >                         1ULL << page_shift);
> > +
> > +               len = order_base_2(query.largest_available_block <<
> > page_shift);
> > +               win_name = DMA64_PROPNAME;
> 
> [1] ....
> 
> 
> > +       } else {
> > +               direct_mapping = true;
> > +               win_name = DIRECT64_PROPNAME;
> > +       }
> > +
> > +       /* DDW + IOMMU on single window may fail if there is any
> > allocation */
> > +       if (default_win_removed && !direct_mapping &&
> > iommu_table_in_use(tbl)) {
> > +               dev_dbg(&dev->dev, "current IOMMU table in use, can't
> > be replaced.\n");
> 
> 
> ... remove !direct_mapping and move to [1]?


sure, done!

> 
> 
> >                 goto out_failed;
> >         }
> >   
> > @@ -1331,8 +1351,7 @@ static bool enable_ddw(struct pci_dev *dev,
> > struct device_node *pdn)
> >                   create.liobn, dn);
> >   
> >         win_addr = ((u64)create.addr_hi << 32) | create.addr_lo;
> > -       win64 = ddw_property_create(DIRECT64_PROPNAME, create.liobn,
> > win_addr,
> > -                                   page_shift, len);
> > +       win64 = ddw_property_create(win_name, create.liobn, win_addr,
> > page_shift, len);
> >         if (!win64) {
> >                 dev_info(&dev->dev,
> >                          "couldn't allocate property, property name,
> > or value\n");
> > @@ -1350,12 +1369,47 @@ static bool enable_ddw(struct pci_dev *dev,
> > struct device_node *pdn)
> >         if (!window)
> >                 goto out_del_prop;
> >   
> > -       ret = walk_system_ram_range(0, memblock_end_of_DRAM() >>
> > PAGE_SHIFT,
> > -                       win64->value,
> > tce_setrange_multi_pSeriesLP_walk);
> > -       if (ret) {
> > -               dev_info(&dev->dev, "failed to map direct window for
> > %pOF: %d\n",
> > -                        dn, ret);
> > -               goto out_del_list;
> > +       if (direct_mapping) {
> > +               /* DDW maps the whole partition, so enable direct DMA
> > mapping */
> > +               ret = walk_system_ram_range(0, memblock_end_of_DRAM()
> > >> PAGE_SHIFT,
> > +                                           win64->value,
> > tce_setrange_multi_pSeriesLP_walk);
> > +               if (ret) {
> > +                       dev_info(&dev->dev, "failed to map direct
> > window for %pOF: %d\n",
> > +                                dn, ret);
> > +                       goto out_del_list;
> > +               }
> > +       } else {
> > +               struct iommu_table *newtbl;
> > +               int i;
> > +
> > +               /* New table for using DDW instead of the default DMA
> > window */
> > +               newtbl = iommu_pseries_alloc_table(pci->phb->node);
> > +               if (!newtbl) {
> > +                       dev_dbg(&dev->dev, "couldn't create new IOMMU
> > table\n");
> > +                       goto out_del_list;
> > +               }
> > +
> > +               for (i = 0; i < ARRAY_SIZE(pci->phb->mem_resources);
> > i++) {
> > +                       const unsigned long mask = IORESOURCE_MEM_64
> > | IORESOURCE_MEM;
> > +
> > +                       /* Look for MMIO32 */
> > +                       if ((pci->phb->mem_resources[i].flags & mask)
> > == IORESOURCE_MEM)
> > +                               break;
> 
> What if there is no IORESOURCE_MEM? pci->phb->mem_resources[i].start 
> below will have garbage.



Yeah, that makes sense. I will add this lines after 'for':

if (i == ARRAY_SIZE(pci->phb->mem_resources)) {
 iommu_tce_table_put(newtbl);
 goto out_del_list;
}

What do you think?


> 
> 
> > +               }
> > +
> > +               _iommu_table_setparms(newtbl, pci->phb->bus->number,
> > create.liobn, win_addr,
> > +                                     1UL << len, page_shift, 0,
> > &iommu_table_lpar_multi_ops);
> > +               iommu_init_table(newtbl, pci->phb->node, pci->phb-
> > >mem_resources[i].start,
> > +                                pci->phb->mem_resources[i].end);
> > +
> > +               if (default_win_removed)
> > +                       iommu_tce_table_put(tbl);
> 
> 
> iommu_tce_table_put() should have been called when the window was
> removed.
> 
> Also after some thinking - what happens if there were 2 devices in the 
> PE and one requested 64bit DMA? This will only update 
> set_iommu_table_base() for the 64bit one but not for the other.
>
> I think the right thing to do is:
> 
> 1. check if table[0] is in use, if yes => fail (which this does
> already)
> 
> 2. remove default dma window but keep the iommu_table struct with one
> change - set it_size to 0 (and free it_map) so the 32bit device won't
> look at a stale structure and think there is some window (imaginery 
> situation for phyp but easy to recreate in qemu).
> 
> 3. use table[1] for newly created indirect DDW window.
> 
> 4. change get_iommu_table_base() to return a usable table (or may be
> not 
> needed?).
> 
> If this sounds reasonable (does it?),

Looks ok, I will try your suggestion. 
I was not aware of how pci->table_group->tables[] worked, so I replaced
pci->table_group->tables[0] with the new tbl, while moving the older in
pci->table_group->tables[1].
(4) get_iommu_table_base() does not seem to need update, as it returns
the tlb set by set_iommu_table_base() which is already called in the
!direct_mapping path in current patch.

>  the question is now if you have
> time to do that and the hardware to test that, or I'll have to finish
> the work :)

Sorry, for some reason part of this got lost in Evolution mail client.

If possible, I do want to finish this work, and I am talking to IBM
Virt people in order to get testing HW.

> 
> 
> > +               else
> > +                       pci->table_group->tables[1] = tbl;
> 
> 
> What is this for?

I was thinking of adding the older table to pci->table_group->tables[1]
while keeping the newer table on pci->table_group->tables[0].
This did work, but I think your suggestion may work better.

Best regards,
Leonardo Bras