Non-SGL transport mode warnings are set to dev_warn_once will cause confusion

[Keith Busch]

On Thu, Apr 09, 2026 at 04:46:37PM +0800, AlanCui4080 wrote:
> See 6fad84a (nvme-pci: use sgls for all user requests if possible). In the 
> kernel, those warnings are printed using `dev warn once`. This means that if 
> multiple devices in the system do not support SGLs (most consumer-grade 
> devices do not support them), only one warning for only one device will be 
> printed.
> 
> This asymmetry can be misleading to users. If all devices in the system report 
> the same issue, it might not be a problem, but if only one device reports it, 
> it might (especially since I have two identical drives). Is it possible to 
> move this warning to the device initialization phase so print it for each 
> device? Or, since we cannot resolve the issue of consumer-grade devices not 
> supporting SGL, should it be downgraded to an informational warning?

Fine with me. The warning was added in response to people filing CVE's
against the driver as a sort of acknowledgement that yeah, this
interface can't validate transfer lengths under these conditions, so
we're trusting the user isn't abusing it. A sort of nudge that perhaps
controller vendors might consider supporting the safer option.

Anyway, it's fine with me to move the message and make it less scary.
How about this:

---
diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index b42d8768d2979..b6aec0e3fbfb8 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -3744,6 +3744,10 @@ int nvme_init_ctrl_finish(struct nvme_ctrl *ctrl, bool was_suspended)
 		ret = nvme_hwmon_init(ctrl);
 		if (ret == -EINTR)
 			return ret;
+
+		if (!nvme_ctrl_sgl_supported(ctrl))
+			dev_info(ctrl->device,
+				"passthrough uses implicit buffer lengths\n");
 	}
 
 	clear_bit(NVME_CTRL_DIRTY_CAPABILITY, &ctrl->flags);
diff --git a/drivers/nvme/host/ioctl.c b/drivers/nvme/host/ioctl.c
index 8844bbd395159..e9eecdd54d5ed 100644
--- a/drivers/nvme/host/ioctl.c
+++ b/drivers/nvme/host/ioctl.c
@@ -125,16 +125,8 @@ static int nvme_map_user_request(struct request *req, u64 ubuffer,
 	struct bio *bio = NULL;
 	int ret;
 
-	if (!nvme_ctrl_sgl_supported(ctrl))
-		dev_warn_once(ctrl->device, "using unchecked data buffer\n");
-	if (has_metadata) {
-		if (!supports_metadata)
-			return -EINVAL;
-
-		if (!nvme_ctrl_meta_sgl_supported(ctrl))
-			dev_warn_once(ctrl->device,
-				      "using unchecked metadata buffer\n");
-	}
+	if (has_metadata && !supports_metadata)
+		return -EINVAL;
 
 	if (iter)
 		ret = blk_rq_map_user_iov(q, req, NULL, iter, GFP_KERNEL);
--