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

["Zhang, AlvinX" <alvinx.zhang@intel.com>]

> -----Original Message-----
> From: David Marchand <david.marchand@redhat.com>
> Sent: Friday, July 10, 2020 5:54 PM
> To: Zhang, AlvinX <alvinx.zhang@intel.com>
> Cc: dev <dev@dpdk.org>; Xing, Beilei <beilei.xing@intel.com>; Guo, Jia
> <jia.guo@intel.com>
> Subject: Re: [dpdk-dev] [PATCH] bus/pci: fix mmap PCI resource
> 
> 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.
> >
> > Fixes: 2fd3567e5425 ("pci: use OS generic memory mapping functions")
> > Cc: talshn@mellanox.com
> >
> > Signed-off-by: Alvin Zhang <alvinx.zhang@intel.com>
> > ---
> >  drivers/bus/pci/linux/pci_vfio.c | 12 +++++++++++-
> >  1 file changed, 11 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/bus/pci/linux/pci_vfio.c
> > b/drivers/bus/pci/linux/pci_vfio.c
> > index fdeb9a8..9143bfc 100644
> > --- 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?
> 

If the misx-table size is equal to the bar size, the memreg[0].size and memreg[1].size will be zero at same time although the bar size is not zero

> 
> >         } 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.
> 
> We can cleanup this code later.

The key cause is the value of memreg[0].size is 0


> 
> >                 if (memreg[0].size) {
> >                         /* actual map of first part */
> >                         map_addr = pci_map_resource(bar_addr,
> > vfio_dev_fd,
> > --
> > 1.8.3.1
> >
> 
> 
> Thanks.
> 
> --
> David Marchand