[RFC v2 07/10] nvme: enhance max supported LBA format check

[Luis Chamberlain <mcgrof@kernel.org>]

Only pure-iomap configurations, systems where CONFIG_BUFFER_HEAD is
disabled can enable NVMe devices with LBA formats with a blocksize
larger then the PAGE_SIZE.

Systems with buffer-heads enabled cannot currently make use of these
devices, but this will eventually get fixed. We cap the max supported
LBA format to 19, 512 KiB as support for 1 MiB LBA format still needs
some work.

Also, add a debug module parameter nvme_core.debug_large_lbas to enable
folks to shoot themselves on their foot though if they want to test
and expand support beyond what is supported, only to be used on
pure-iomap configurations.

Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Signed-off-by: Pankaj Raghav <p.raghav@samsung.com>
---
 drivers/nvme/host/core.c | 34 +++++++++++++++++++++++++++++-----
 1 file changed, 29 insertions(+), 5 deletions(-)

diff --git a/drivers/nvme/host/core.c b/drivers/nvme/host/core.c
index f3a01b79148c..0365f260c514 100644
--- a/drivers/nvme/host/core.c
+++ b/drivers/nvme/host/core.c
@@ -88,6 +88,10 @@ module_param(apst_secondary_latency_tol_us, ulong, 0644);
 MODULE_PARM_DESC(apst_secondary_latency_tol_us,
 	"secondary APST latency tolerance in us");
 
+static bool debug_large_lbas;
+module_param(debug_large_lbas, bool, 0644);
+MODULE_PARM_DESC(debug_large_lbas, "allow LBAs > PAGE_SIZE");
+
 /*
  * nvme_wq - hosts nvme related works that are not reset or delete
  * nvme_reset_wq - hosts nvme reset works
@@ -1878,6 +1882,29 @@ static void nvme_set_queue_limits(struct nvme_ctrl *ctrl,
 	blk_queue_write_cache(q, vwc, vwc);
 }
 
+/* XXX: shift 20 (1 MiB LBA) crashes on pure-iomap */
+#define NVME_MAX_SHIFT_SUPPORTED 19
+
+static bool nvme_lba_shift_supported(struct nvme_ns *ns)
+{
+	if (ns->lba_shift <= PAGE_SHIFT)
+		return true;
+
+	if (IS_ENABLED(CONFIG_BUFFER_HEAD))
+		return false;
+
+	if (ns->lba_shift <= NVME_MAX_SHIFT_SUPPORTED)
+		return true;
+
+	if (debug_large_lbas) {
+		dev_warn(ns->ctrl->device,
+			"forcibly allowing LBAS > 1 MiB due to nvme_core.debug_large_lbas -- use at your own risk\n");
+		return true;
+	}
+
+	return false;
+}
+
 static void nvme_update_disk_info(struct gendisk *disk,
 		struct nvme_ns *ns, struct nvme_id_ns *id)
 {
@@ -1885,13 +1912,10 @@ static void nvme_update_disk_info(struct gendisk *disk,
 	u32 bs = 1U << ns->lba_shift;
 	u32 atomic_bs, phys_bs, io_opt = 0;
 
-	/*
-	 * The block layer can't support LBA sizes larger than the page size
-	 * yet, so catch this early and don't allow block I/O.
-	 */
-	if (ns->lba_shift > PAGE_SHIFT) {
+	if (!nvme_lba_shift_supported(ns)) {
 		capacity = 0;
 		bs = (1 << 9);
+		dev_warn(ns->ctrl->device, "I'm sorry dave, I'm afraid I can't do that\n");
 	}
 
 	blk_integrity_unregister(disk);
-- 
2.39.2