nvme: implement the DEAC bit for the Write Zeroes command

While the specification allows devices to either deallocate data
or to actually write zeroes on any Write Zeroes command, many SSDs
only do the sensible thing and deallocate data when the DEAC bit
is specific.  Set it when it is supported and the caller doesn't
explicitly opt out of deallocation.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Keith Busch <kbusch@kernel.org>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>

drivers/nvme/host/core.c

@@ -850,8 +850,11 @@ static inline blk_status_t nvme_setup_write_zeroes(struct nvme_ns *ns,
 	cmnd->write_zeroes.length =
 		cpu_to_le16((blk_rq_bytes(req) >> ns->lba_shift) - 1);
 
+	if (!(req->cmd_flags & REQ_NOUNMAP) && (ns->features & NVME_NS_DEAC))
+		cmnd->write_zeroes.control |= cpu_to_le16(NVME_WZ_DEAC);
+
 	if (nvme_ns_has_pi(ns)) {
-		cmnd->write_zeroes.control = cpu_to_le16(NVME_RW_PRINFO_PRACT);
+		cmnd->write_zeroes.control |= cpu_to_le16(NVME_RW_PRINFO_PRACT);
 
 		switch (ns->pi_type) {
 		case NVME_NS_DPS_PI_TYPE1:
@@ -2003,6 +2006,14 @@ static int nvme_update_ns_info_block(struct nvme_ns *ns,
 		}
 	}
 
+	/*
+	 * Only set the DEAC bit if the device guarantees that reads from
+	 * deallocated data return zeroes.  While the DEAC bit does not
+	 * require that, it must be a no-op if reads from deallocated data
+	 * do not return zeroes.
+	 */
+	if ((id->dlfeat & 0x7) == 0x1 && (id->dlfeat & (1 << 3)))
+		ns->features |= NVME_NS_DEAC;
 	set_disk_ro(ns->disk, nvme_ns_is_readonly(ns, info));
 	set_bit(NVME_NS_READY, &ns->flags);
 	blk_mq_unfreeze_queue(ns->disk->queue);

drivers/nvme/host/nvme.h

@@ -455,6 +455,7 @@ static inline bool nvme_ns_head_multipath(struct nvme_ns_head *head)
 enum nvme_ns_features {
 	NVME_NS_EXT_LBAS = 1 << 0, /* support extended LBA format */
 	NVME_NS_METADATA_SUPPORTED = 1 << 1, /* support getting generated md */
+	NVME_NS_DEAC,		/* DEAC bit in Write Zeores supported */
 };
 
 struct nvme_ns {

include/linux/nvme.h

@@ -964,6 +964,7 @@ enum {
 	NVME_RW_PRINFO_PRCHK_GUARD	= 1 << 12,
 	NVME_RW_PRINFO_PRACT		= 1 << 13,
 	NVME_RW_DTYPE_STREAMS		= 1 << 4,
+	NVME_WZ_DEAC			= 1 << 9,
 };
 
 struct nvme_dsm_cmd {