Re: [Xen-devel] [RFC][PATCH 12/13] hvmloader/pci: skip reserved ranges

["Chen, Tiejun" <tiejun.chen@xxxxxxxxx>]

On 2015/5/15 16:31, Jan Beulich wrote:
> > > > On 15.05.15 at 10:16, <tiejun.chen@xxxxxxxxx> wrote:
> > On 2015/5/15 15:44, Jan Beulich wrote:
> > > > > > On 15.05.15 at 09:34, <tiejun.chen@xxxxxxxxx> wrote:
> > > > So I think we may need to adjust pci_mem_start like this,
> > > >
> > > > @@ -301,6 +301,19 @@ void pci_setup(void)
> > > >                 pci_mem_start <<= 1;
> > > >         }
> > > >
> > > > +    /* Relocate PCI memory that overlaps reserved space, like RDM. */
> > > > +    for ( j = 0; j < memory_map.nr_map ; j++ )
> > > > +    {
> > > > +        if ( memory_map.map[j].type != E820_RAM )
> > > > +        {
> > > > +            reserved_end = memory_map.map[j].addr + memory_map.map[j].size;
> > > > +            if ( check_overlap(pci_mem_start, pci_mem_end,
> > > > +                               memory_map.map[j].addr,
> > > > +                               memory_map.map[j].size) )
> > > > +                pci_mem_start -= memory_map.map[j].size >> PAGE_SHIFT;
> > > > +        }
> > > > +    }
> > > > +
> > > >         if ( mmio_total > (pci_mem_end - pci_mem_start) )
> > > >         {
> > > >             printf("Low MMIO hole not large enough for all devices,"
> > > >
> > > > Right?
> > > I think that gets you in the right direction, but isn't enough, as it
> > > doesn't account for (unavoidable) gaps (BARs are always a power
> > > of 2 in size and accordingly aligned).
> > Right.
> >
> > But as you see, we always take this action, >> PAGE_SHIFT, so this means
> > its always a sort of power of 2.
> No, certainly not.
rdm start or size? Or anything else I'm missing?

> > Additionally, lets go back here,
> >
> >           if ( (base < resource->base) || (base > resource->max) )
> >           {
> >               printf("pci dev %02x:%x bar %02x size "PRIllx": no space for "
> >                      "resource!\n", devfn>>3, devfn&7, bar_reg,
> >                      PRIllx_arg(bar_sz));
> >               continue;
> >           }
> >
> > I mean even without rdm, the original codes don't consider handling this
> > lack of space from a alignment in advance, right?
> Correct. But your change increases the chances of this getting
> used. Also I think you may want to carefully look at under what
> conditions this path gets taken without and with your patches.
Sure.

I think I can record that max bar_sz to improve this like,

@@ -60,7 +60,7 @@ void pci_setup(void)
         uint64_t bar_sz;
     } *bars = (struct bars *)scratch_start;
     unsigned int i, j, nr_bars = 0;
-    uint64_t mmio_hole_size = 0, reserved_end;
+    uint64_t mmio_hole_size = 0, reserved_end, max_bar_sz = 0;

     const char *s;
     /*
@@ -226,6 +226,8 @@ void pci_setup(void)
             bars[i].devfn   = devfn;
             bars[i].bar_reg = bar_reg;
             bars[i].bar_sz  = bar_sz;
+            if ( bar_sz > max_bar_sz )
+                max_bar_sz = bar_sz;

             if ( ((bar_data & PCI_BASE_ADDRESS_SPACE) ==
                   PCI_BASE_ADDRESS_SPACE_MEMORY) ||
@@ -311,6 +313,8 @@ void pci_setup(void)
                                memory_map.map[j].addr,
                                memory_map.map[j].size) )
                 pci_mem_start -= memory_map.map[j].size >> PAGE_SHIFT;
+                pci_mem_start = (pci_mem_start + max_bar_sz - 1) &
+                                    ~(uint64_t)(max_bar_sz - 1);
         }
     }


Note you also can take close look at this change in next revision if 
this is not that bad with your glance :)
Thanks
Tiejun

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