Re: [dpdk-dev] [PATCH] bus/pci: fix mmap PCI resource

[Thomas Monjalon <thomas@monjalon.net>]

10/07/2020 11:54, David Marchand:
> On Wed, Jul 8, 2020 at 11:26 AM <alvinx.zhang@intel.com> wrote:
> > From: Alvin Zhang <alvinx.zhang@intel.com>
> >
> > When mapping a PCI BAR containing an MSI-X table, some devices do not
> > need to actually map this BAR or only need to map part of them, which
> > may cause the mapping to fail. Now some checks are added and a non-NULL
> > initial value is set to the variable to avoid this situation.

Note: this regression would not have happened if we had some CI tests
for simple device probing.
Please let's invest more in CI.


> > Fixes: 2fd3567e5425 ("pci: use OS generic memory mapping functions")
> > Cc: talshn@mellanox.com

No he was not Cc in the thread. Same for Anatoly.
Adding more people in Cc...

> > Signed-off-by: Alvin Zhang <alvinx.zhang@intel.com>
> > ---
> > --- a/drivers/bus/pci/linux/pci_vfio.c
> > +++ b/drivers/bus/pci/linux/pci_vfio.c
> > @@ -547,6 +547,14 @@
> >                         bar_index,
> >                         memreg[0].offset, memreg[0].size,
> >                         memreg[1].offset, memreg[1].size);
> > +
> > +               if (memreg[0].size == 0 && memreg[1].size == 0) {
> > +                       /* No need to map this BAR */
> > +                       RTE_LOG(DEBUG, EAL, "Skipping BAR%d\n", bar_index);
> > +                       bar->size = 0;
> > +                       bar->addr = 0;
> > +                       return 0;
> > +               }
> 
> We already have a check on bar size == 0.
> Why would we have this condition?
> Broken hw?
> 
> 
> >         } else {
> >                 memreg[0].offset = bar->offset;
> >                 memreg[0].size = bar->size;
> > @@ -556,7 +564,9 @@
> >         bar_addr = mmap(bar->addr, bar->size, 0, MAP_PRIVATE |
> >                         MAP_ANONYMOUS | additional_flags, -1, 0);
> >         if (bar_addr != MAP_FAILED) {
> > -               void *map_addr = NULL;
> > +               /* Set non NULL initial value for in case of no PCI mapping */
> > +               void *map_addr = bar_addr;
> > +
> 
> It took me some time to understand this code...
> Anyway, we have a regression in the librte_pci.
> This is where the fix should be.

Yes, I am going to send a fix.

> We can cleanup this code later.

Yes please, this function isn't understandable and lack of comments.
Anatoly please?