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

["Xia, Chenbo" <chenbo.xia@intel.com>]

> -----Original Message-----
> From: Zhang, AlvinX <alvinx.zhang@intel.com>
> Sent: Thursday, July 9, 2020 1:14 PM
> To: Xia, Chenbo <chenbo.xia@intel.com>; dev@dpdk.org
> Cc: David Marchand <david.marchand@redhat.com>; Tal Shnaiderman
> <talshn@mellanox.com>; Burakov, Anatoly <anatoly.burakov@intel.com>;
> thomas@monjalon.net
> Subject: RE: [dpdk-dev] [PATCH] bus/pci: fix mmap PCI resource
> 
> Hi Chenbo,
> 
> Thanks your comments.
> 
> > -----Original Message-----
> > From: Xia, Chenbo <chenbo.xia@intel.com>
> > Sent: Wednesday, July 8, 2020 9:58 PM
> > To: Zhang, AlvinX <alvinx.zhang@intel.com>; dev@dpdk.org
> > Cc: Xing, Beilei <beilei.xing@intel.com>; Guo, Jia
> > <jia.guo@intel.com>; David Marchand <david.marchand@redhat.com>; Tal
> > Shnaiderman <talshn@mellanox.com>; Burakov, Anatoly
> > <anatoly.burakov@intel.com>; thomas@monjalon.net
> > Subject: RE: [dpdk-dev] [PATCH] bus/pci: fix mmap PCI resource
> >
> > Hi Alvin,
> >
> > CC the maintainers. Comments below.
> >
> > > -----Original Message-----
> > > From: dev <dev-bounces@dpdk.org> On Behalf Of alvinx.zhang@intel.com
> > > Sent: Wednesday, July 8, 2020 5:25 PM
> > > To: dev@dpdk.org
> > > Cc: Xing, Beilei <beilei.xing@intel.com>; Guo, Jia
> > > <jia.guo@intel.com>
> > > Subject: [dpdk-dev] [PATCH] bus/pci: fix mmap PCI resource
> > >
> > > 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;
> > > +		}
> >
> > I'm not sure if this corner case will happen. If you confirmed it, Just ignore this.
> 
> In theory, it is entirely possible if the misx-table size is equal to the bar size.
> 
> >
> > >  	} 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;
> > > +
> >
> > I see the issue that this patch wants to fix is based on an old kernel.
> > In older vfio-pci kernel module, MSI related reg cannot be mmaped in
> > userspace while in newer kernel it can be. That's why sometimes it
> > cannot be reproduced
> > (https://bugs.dpdk.org/show_bug.cgi?id=503)
> >
> > So under the condition of old kernel, there could be an example that
> > Memreg 0 has size 0 but Memreg 1 has non-zero size, which leads to
> > Memreg 1 cannot be mmaped.
> 
> Yes, it is.
> 
> >
> > So I'm fine with this part of code change. As this issue is blocking
> > test, we should do fast confirm and review.
> >
> > Thanks,
> > Chenbo
> >
> > >  		if (memreg[0].size) {
> > >  			/* actual map of first part */
> > >  			map_addr = pci_map_resource(bar_addr, vfio_dev_fd,
> > > --
> > > 1.8.3.1

Acked-by: Chenbo Xia <chenbo.xia@intel.com>