On 12/07/2017 03:45, Tan, Jianfeng wrote:
-----Original Message-----
From: Gonzalez Monroy, Sergio
Sent: Tuesday, July 11, 2017 7:36 PM
To: Tan, Jianfeng; Stephen Hemminger; dev@dpdk.org
Subject: Re: [dpdk-dev] [RFC] pci: force address of mappings in secondary
process
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 did by check /proc/self/maps.
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.
IMO, that's not the target of this RFC. The target is to solve the situation
(in current primary/secondary model) that kernel will not use the addr even
there's no VMA on that addr. This is my understanding, Stephen, please correct
me if I'm wrong.
The point I was trying to make is, that you do not know if there is a
mapping or not in that address, and by using MAP_FIXED it will unmap
whatever was in there before.
So unless you parse /proc/self/maps and check that the VMA range is not
being used, forcing MAP_FIXED is not safe.
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.
This is another problem.
It is the same problem, VMA ranges that we need to map being already used.
Thanks,
Sergio
The proposal for new secondary process model would solve these issues:
http://dpdk.org/ml/archives/dev/2017-May/066147.html
And yes, this might happen to solve the targeted issue in this RFC. But before
the new model is out, this patch seems a workable way for the original issue.
Thanks,
Jianfeng
Thanks,
Sergio
