Re: [net-next][PATCH v2 1/2] rds: handle unsupported rdma request to fs dax memory
From: Leon Romanovsky <leon@kernel.org>
Date: 2019-05-01 17:28:30
On Mon, Apr 29, 2019 at 04:37:19PM -0700, Santosh Shilimkar wrote:
quoted hunk ↗ jump to hunk
From: Hans Westgaard Ry <redacted> RDS doesn't support RDMA on memory apertures that require On Demand Paging (ODP), such as FS DAX memory. User applications can try to use RDS to perform RDMA over such memories and since it doesn't report any failure, it can lead to unexpected issues like memory corruption when a couple of out of sync file system operations like ftruncate etc. are performed. The patch adds a check so that such an attempt to RDMA to/from memory apertures requiring ODP will fail. Reviewed-by: Håkon Bugge <redacted> Reviewed-tested-by: Zhu Yanjun [off-list ref] Signed-off-by: Hans Westgaard Ry <redacted> Signed-off-by: Santosh Shilimkar <redacted> --- net/rds/rdma.c | 5 +++-- 1 file changed, 3 insertions(+), 2 deletions(-)diff --git a/net/rds/rdma.c b/net/rds/rdma.c index 182ab84..e0a6b72 100644 --- a/net/rds/rdma.c +++ b/net/rds/rdma.c@@ -158,8 +158,9 @@ static int rds_pin_pages(unsigned long user_addr, unsigned int nr_pages, { int ret; - ret = get_user_pages_fast(user_addr, nr_pages, write, pages); - + /* get_user_pages return -EOPNOTSUPP for fs_dax memory */ + ret = get_user_pages_longterm(user_addr, nr_pages, + write, pages, NULL);
I'm not RDS expert, but from what I see in net/rds/rdma.c and this code, you tried to mimic ib_umem_get() without protection, checks and native ODP, FS and DAX supports. The real way to solve your ODP problem will require to extend ib_umem_get() to work for kernel ULPs too and use it instead of get_user_pages(). We are working on that and it is in internal review now. It is applicable if underneath your RDS code, there is IB code, in case there is no such layer, you shouldn't return IB_DEVICE_ON_DEMAND_PAGING capability to user space and return EINVAL for every attempt to create such ODP MR. Thanks
if (ret >= 0 && ret < nr_pages) {
while (ret--)
put_page(pages[ret]);
--
1.9.1