On 2021-05-02 7:29 p.m., John Hubbard wrote:

On 4/8/21 10:01 AM, Logan Gunthorpe wrote:

quoted

Introduce a supports_pci_p2pdma() operation in nvme_ctrl_ops to
replace the fixed NVME_F_PCI_P2PDMA flag such that the dma_map_ops
flags can be checked for PCI P2PDMA support.

Signed-off-by: Logan Gunthorpe <logang@deltatee.com>
---
  drivers/nvme/host/core.c |  3 ++-
  drivers/nvme/host/nvme.h |  2 +-
  drivers/nvme/host/pci.c  | 11 +++++++++--
  3 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index 0896e21642be..223419454516 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c

@@ -3907,7 +3907,8 @@ static void nvme_alloc_ns(struct nvme_ctrl *ctrl, unsigned nsid,
  		blk_queue_flag_set(QUEUE_FLAG_STABLE_WRITES, ns->queue);
  
  	blk_queue_flag_set(QUEUE_FLAG_NONROT, ns->queue);
-	if (ctrl->ops->flags & NVME_F_PCI_P2PDMA)
+	if (ctrl->ops->supports_pci_p2pdma &&
+	    ctrl->ops->supports_pci_p2pdma(ctrl))

This is a little excessive, as I suspected. How about providing a
default .supports_pci_p2pdma routine that returns false, so that
the op is always available (non-null)? By "default", maybe that
means either requiring an init_the_ops_struct() routine to be
used, and/or checking all the users of struct nvme_ctrl_ops.

Honestly that sounds much more messy to me than simply checking if it's
NULL before using it (which is a common, accepted pattern for ops).

Another idea: maybe you don't really need a bool .supports_pci_p2pdma()
routine at all, because the existing .flags really is about right.
You just need the flags to be filled in dynamically. So, do that
during nvme_pci setup/init time: that's when this module would call
dma_pci_p2pdma_supported().

If the flag is filled in dynamically, then the ops struct would have to
be non-constant. Ops structs should be constant for security reasons.

Logan

_______________________________________________
Linux-nvme mailing list
Linux-nvme@lists.infradead.org
http://lists.infradead.org/mailman/listinfo/linux-nvme