From e6c1e862b2b8150a419f4208e5bd7749662b16a1 Mon Sep 17 00:00:00 2001
From: Jonathan Bell <jonathan@raspberrypi.com>
Date: Thu, 20 Jun 2024 14:31:20 +0100
Subject: [PATCH 1167/1215] mmc: restrict posted write counts for SD cards in
 CQ mode

Command Queueing requires Write Cache and Power off Notification support
from the card - but using the write cache forms a contract with the host
whereby the card expects to be told about impending power-down.

The implication is that (for performance) the card can do unsafe things
with pending write data - including reordering what gets committed to
nonvolatile storage at what time.

Exposed SD slots and platforms powered by hotpluggable means (i.e.
Raspberry Pis) can't guarantee that surprise removal won't happen.

To limit the scope for cards to invent new ways to trash filesystems,
limit pending writes to 1 (equivalent to the non-CQ behaviour).

Signed-off-by: Jonathan Bell <jonathan@raspberrypi.com>
---
 drivers/mmc/core/block.c | 11 +++++++++--
 drivers/mmc/core/mmc.c   |  1 +
 drivers/mmc/core/queue.c |  9 +++++++++
 drivers/mmc/core/queue.h |  1 +
 drivers/mmc/core/sd.c    |  8 ++++++++
 include/linux/mmc/card.h |  2 ++
 6 files changed, 30 insertions(+), 2 deletions(-)

--- a/drivers/mmc/core/block.c
+++ b/drivers/mmc/core/block.c
@@ -1555,6 +1555,8 @@ static void mmc_blk_cqe_complete_rq(stru
 
 	spin_lock_irqsave(&mq->lock, flags);
 
+	if (req_op(req) == REQ_OP_WRITE)
+		mq->pending_writes--;
 	mq->in_flight[issue_type] -= 1;
 
 	put_card = (mmc_tot_in_flight(mq) == 0);
@@ -2071,6 +2073,8 @@ static void mmc_blk_mq_complete_rq(struc
 	struct mmc_queue_req *mqrq = req_to_mmc_queue_req(req);
 	unsigned int nr_bytes = mqrq->brq.data.bytes_xfered;
 
+	if (req_op(req) == REQ_OP_WRITE)
+		mq->pending_writes--;
 	if (nr_bytes) {
 		if (blk_update_request(req, BLK_STS_OK, nr_bytes))
 			blk_mq_requeue_request(req, true);
@@ -2165,13 +2169,16 @@ static void mmc_blk_mq_poll_completion(s
 	mmc_blk_urgent_bkops(mq, mqrq);
 }
 
-static void mmc_blk_mq_dec_in_flight(struct mmc_queue *mq, enum mmc_issue_type issue_type)
+static void mmc_blk_mq_dec_in_flight(struct mmc_queue *mq, enum mmc_issue_type issue_type,
+				     struct request *req)
 {
 	unsigned long flags;
 	bool put_card;
 
 	spin_lock_irqsave(&mq->lock, flags);
 
+	if (req_op(req) == REQ_OP_WRITE)
+		mq->pending_writes--;
 	mq->in_flight[issue_type] -= 1;
 
 	put_card = (mmc_tot_in_flight(mq) == 0);
@@ -2205,7 +2212,7 @@ static void mmc_blk_mq_post_req(struct m
 			blk_mq_complete_request(req);
 	}
 
-	mmc_blk_mq_dec_in_flight(mq, issue_type);
+	mmc_blk_mq_dec_in_flight(mq, issue_type, req);
 }
 
 void mmc_blk_mq_recovery(struct mmc_queue *mq)
--- a/drivers/mmc/core/mmc.c
+++ b/drivers/mmc/core/mmc.c
@@ -1922,6 +1922,7 @@ static int mmc_init_card(struct mmc_host
 				pr_info("%s: Host Software Queue enabled\n",
 					mmc_hostname(host));
 			}
+			card->max_posted_writes = card->ext_csd.cmdq_depth;
 		}
 	}
 
--- a/drivers/mmc/core/queue.c
+++ b/drivers/mmc/core/queue.c
@@ -268,6 +268,11 @@ static blk_status_t mmc_mq_queue_rq(stru
 			spin_unlock_irq(&mq->lock);
 			return BLK_STS_RESOURCE;
 		}
+		if (host->cqe_enabled && req_op(req) == REQ_OP_WRITE &&
+		    mq->pending_writes >= card->max_posted_writes) {
+			spin_unlock_irq(&mq->lock);
+			return BLK_STS_RESOURCE;
+		}
 		break;
 	default:
 		/*
@@ -284,6 +289,8 @@ static blk_status_t mmc_mq_queue_rq(stru
 	/* Parallel dispatch of requests is not supported at the moment */
 	mq->busy = true;
 
+	if (req_op(req) == REQ_OP_WRITE)
+		mq->pending_writes++;
 	mq->in_flight[issue_type] += 1;
 	get_card = (mmc_tot_in_flight(mq) == 1);
 	cqe_retune_ok = (mmc_cqe_qcnt(mq) == 1);
@@ -323,6 +330,8 @@ static blk_status_t mmc_mq_queue_rq(stru
 		bool put_card = false;
 
 		spin_lock_irq(&mq->lock);
+		if (req_op(req) == REQ_OP_WRITE)
+			mq->pending_writes--;
 		mq->in_flight[issue_type] -= 1;
 		if (mmc_tot_in_flight(mq) == 0)
 			put_card = true;
--- a/drivers/mmc/core/queue.h
+++ b/drivers/mmc/core/queue.h
@@ -79,6 +79,7 @@ struct mmc_queue {
 	struct request_queue	*queue;
 	spinlock_t		lock;
 	int			in_flight[MMC_ISSUE_MAX];
+	int			pending_writes;
 	unsigned int		cqe_busy;
 #define MMC_CQE_DCMD_BUSY	BIT(0)
 	bool			busy;
--- a/drivers/mmc/core/sd.c
+++ b/drivers/mmc/core/sd.c
@@ -1120,6 +1120,14 @@ static int sd_parse_ext_reg_perf(struct
 		pr_debug("%s: Command Queue supported depth %u\n",
 			 mmc_hostname(card->host),
 			 card->ext_csd.cmdq_depth);
+		/*
+		 * If CQ is enabled, there is a contract between host and card such that VDD will
+		 * be maintained and removed only if a power off notification is provided.
+		 * An SD card in an accessible slot means surprise removal is a possibility.
+		 * As a middle ground, limit max posted writes to 1 unless the card is "hardwired".
+		 */
+		if (mmc_card_is_removable(card->host))
+			card->max_posted_writes = 1;
 	}
 
 	card->ext_perf.fno = fno;
--- a/include/linux/mmc/card.h
+++ b/include/linux/mmc/card.h
@@ -345,6 +345,8 @@ struct mmc_card {
 	unsigned int    nr_parts;
 
 	struct workqueue_struct *complete_wq;	/* Private workqueue */
+
+	unsigned int		max_posted_writes; /* command queue posted write limit */
 };
 
 static inline bool mmc_large_sector(struct mmc_card *card)
