On Tue, 11 Jul 2017 12:35:39 +0100 Sergio Gonzalez Monroy <sergio.gonzalez.mon...@intel.com> wrote:
> On 11/07/2017 02:56, Tan, Jianfeng wrote: > >> -----Original Message----- > >> From: dev [mailto:dev-boun...@dpdk.org] On Behalf Of Stephen > >> Hemminger > >> Sent: Tuesday, July 11, 2017 9:13 AM > >> To: dev@dpdk.org > >> Cc: Stephen Hemminger > >> Subject: [dpdk-dev] [RFC] pci: force address of mappings in secondary > >> process > >> > >> The PCI memory resources in the secondary process should be in > >> the exact same location as the primary process. Otherwise > >> there is a risk of a stray pointer. > >> > >> Not sure if this is right, but it looks like a potential > >> problem. > >> > >> --- > >> lib/librte_eal/common/eal_common_pci_uio.c | 2 +- > >> 1 file changed, 1 insertion(+), 1 deletion(-) > >> > >> diff --git a/lib/librte_eal/common/eal_common_pci_uio.c > >> b/lib/librte_eal/common/eal_common_pci_uio.c > >> index 367a6816dcb8..2156b1a436c4 100644 > >> --- a/lib/librte_eal/common/eal_common_pci_uio.c > >> +++ b/lib/librte_eal/common/eal_common_pci_uio.c > >> @@ -77,7 +77,7 @@ pci_uio_map_secondary(struct rte_pci_device *dev) > >> > >> void *mapaddr = pci_map_resource(uio_res- > >>> maps[i].addr, > >> fd, (off_t)uio_res->maps[i].offset, > >> - (size_t)uio_res->maps[i].size, 0); > >> + (size_t)uio_res->maps[i].size, > >> MAP_FIXED); > >> /* fd is not needed in slave process, close it */ > >> close(fd); > >> if (mapaddr != uio_res->maps[i].addr) { > >> -- > >> 2.11.0 > > +1 for this RFC. I also once encounter such problem, and I use the same way > > to solve it. The addr parameter of mmap() syscall is only a hint instead of > > a must even the VMA is not occupied yet. > > > > Thanks, > > Jianfeng > > How do you know the VMA is not occupied? > > I think the risk here is that the dynamic linker loaded some shared > library in that VMA, and forcing MAP_FIXED is not a safe solution. > What I have observed is that Linux will return a different VMA than the > one hinted when there is already a mapping in the requested/hinted VMA. > > I reckon this is a similar issue as we have with the multi-process model > when we do not get the VMA requested for the huge-pages. > AFAIK we do not have a robust solution for this issue other than restart > the program and hope the dynamic linker does not map anything in the VMA > ranges that we need to map from the primary. This is also assuming that > the application does not allocate memory and maps things before calling > eal_init as it could potentially use VMA ranges that we need in the > secondary process. > > The proposal for new secondary process model would solve these issues: > http://dpdk.org/ml/archives/dev/2017-May/066147.html > > Thanks, > Sergio That proposal defeats some of the isolation of secondary process model. The idea is that secondary could be built separately. It is also overly complex and would make a somewhat fragile part of the DPDK, more difficult.
