On Thu, May 02, 2019 at 10:59:58AM -0700, Santosh Shilimkar wrote: > > > On 5/1/2019 11:18 PM, Leon Romanovsky wrote: > > On Wed, May 01, 2019 at 10:54:50AM -0700, Santosh Shilimkar wrote: > > > On 5/1/2019 12:45 AM, Leon Romanovsky wrote: > > > > On Mon, Apr 29, 2019 at 04:37:20PM -0700, Santosh Shilimkar wrote: > > > > > RDS doesn't support RDMA on memory apertures that require On Demand > > > > > Paging (ODP), such as FS DAX memory. A sysctl is added to indicate > > > > > whether RDMA requiring ODP is supported. > > > > > > > > > > Reviewed-by: H??kon Bugge <haakon.bu...@oracle.com> > > > > > Reviewed-tested-by: Zhu Yanjun <yanjun....@oracle.com> > > > > > Signed-off-by: Hans Westgaard Ry <hans.westgaard...@oracle.com> > > > > > Signed-off-by: Santosh Shilimkar <santosh.shilim...@oracle.com> > > > > > --- > > > > > net/rds/ib.h | 1 + > > > > > net/rds/ib_sysctl.c | 8 ++++++++ > > > > > 2 files changed, 9 insertions(+) > > > > > > > > This sysctl is not needed at all > > > > > > > Its needed for application to check the support of the ODP support > > > feature which in progress. Failing the RDS_GET_MR was just one path > > > and we also support inline MR registration along with message request. > > > > > > Basically application runs on different kernel versions and to be > > > portable, it will check if underneath RDS support ODP and then only > > > use RDMA. If not it will fallback to buffer copy mode. Hope > > > it clarifies. > > > > Using ODP sysctl to determine if to use RDMA or not, looks like very > > problematic approach. How old applications will work in such case > > without knowledge of such sysctl? > > How new applications will distinguish between ODP is not supported, but > > RDMA works? > > > Actually this is not ODP sysctl but really whether RDS supports > RDMA on fs_dax memory or not. I had different name for sysctl but > in internal review it got changed. > > Ignoring the name of the sysctl, here is the application logic. > - If fs_dax sysctl path doesn't exist, no RDMA on FS DAX memory(this > will cover all the older kernels, which doesn't have this patch) > - If fs_dax sysctl path exist and its value is 0, no RDMA on FS > DAX. This will cover kernels which this patch but don't have > actual support for ODP based registration. > - If fs_dax sysctl path exist and its value is 1, RDMA can be > issued on FS DAX memory. This sysctl will be updated to value 1 > once the support gets added. > > Hope it clarifies better now.
Santosh, Thanks for explanation, I have one more question, If I'm author of hostile application and write code to disregard that new sysctl, will any of combinations of kernel/application cause to kernel panic? If not, we don't really need to expose this information, if yes, this sysctl is not enough. Thanks > > Regards, > Santosh
