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

[David Marchand <david.marchand@redhat.com>]

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?


>         } 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.

>                 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