On Wed, Apr 07, 2021 at 01:16:05PM +0300, Gal Pressman wrote:
> The new attribute indicates that the kernel copies DMA pages on fork,
> hence libibverbs' fork support through madvise and MADV_DONTFORK is not
> needed.
>
> The introduced attribute is always reported as supported since the
> kernel has the patch that added the copy-on-fork behavior. This allows
> the userspace library to identify older vs newer kernel versions.
> Extra care should be taken when backporting this patch as it relies on
> the fact that the copy-on-fork patch is merged, hence no check for
> support is added.
>
> Don't backport this patch unless you also have the following series:
> 70e806e4e645 ("mm: Do early cow for pinned pages during fork() for ptes")
> and 4eae4efa2c29 ("hugetlb: do early cow when page pinned on src mm").
>
> Copy-on-fork attribute is read-only, trying to change it through the set
> sys command will result in an error.
>
> Fixes: 70e806e4e645 ("mm: Do early cow for pinned pages during fork() for ptes")
> Fixes: 4eae4efa2c29 ("hugetlb: do early cow when page pinned on src mm")
> Signed-off-by: Gal Pressman <galpress@xxxxxxxxxx>
> ---
> PR was sent:
> https://github.com/linux-rdma/rdma-core/pull/975
>
> Changelog -
> v1->v2: https://lore.kernel.org/linux-rdma/20210405114722.98904-1-galpress@xxxxxxxxxx/
> * Remove nla_put_u8() return value check
> * Add commit hashes to commit message and code comment
> ---
> drivers/infiniband/core/nldev.c | 14 +++++++++++++-
> include/uapi/rdma/rdma_netlink.h | 2 ++
> 2 files changed, 15 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/infiniband/core/nldev.c b/drivers/infiniband/core/nldev.c
> index b8dc002a2478..6b2235926f74 100644
> --- a/drivers/infiniband/core/nldev.c
> +++ b/drivers/infiniband/core/nldev.c
> @@ -146,6 +146,7 @@ static const struct nla_policy nldev_policy[RDMA_NLDEV_ATTR_MAX] = {
> [RDMA_NLDEV_ATTR_UVERBS_DRIVER_ID] = { .type = NLA_U32 },
> [RDMA_NLDEV_NET_NS_FD] = { .type = NLA_U32 },
> [RDMA_NLDEV_SYS_ATTR_NETNS_MODE] = { .type = NLA_U8 },
> + [RDMA_NLDEV_SYS_ATTR_COPY_ON_FORK] = { .type = NLA_U8 },
> };
>
> static int put_driver_name_print_type(struct sk_buff *msg, const char *name,
> @@ -1697,6 +1698,16 @@ static int nldev_sys_get_doit(struct sk_buff *skb, struct nlmsghdr *nlh,
> nlmsg_free(msg);
> return err;
> }
> +
> + /*
> + * Copy-on-fork is supported.
> + * See commits:
> + * 70e806e4e645 ("mm: Do early cow for pinned pages during fork() for ptes")
> + * 4eae4efa2c29 ("hugetlb: do early cow when page pinned on src mm")
> + * for more details. Don't backport this without them.
> + */
> + nla_put_u8(msg, RDMA_NLDEV_SYS_ATTR_COPY_ON_FORK, 1);
> +
> nlmsg_end(msg, nlh);
> return rdma_nl_unicast(sock_net(skb->sk), msg, NETLINK_CB(skb).portid);
> }
> @@ -1710,7 +1721,8 @@ static int nldev_set_sys_set_doit(struct sk_buff *skb, struct nlmsghdr *nlh,
>
> err = nlmsg_parse(nlh, 0, tb, RDMA_NLDEV_ATTR_MAX - 1,
> nldev_policy, extack);
> - if (err || !tb[RDMA_NLDEV_SYS_ATTR_NETNS_MODE])
> + if (err || !tb[RDMA_NLDEV_SYS_ATTR_NETNS_MODE] ||
> + tb[RDMA_NLDEV_SYS_ATTR_COPY_ON_FORK])
Why do we fail if user supplies RDMA_NLDEV_SYS_ATTR_COPY_ON_FORK?
Thanks
