linux-kernel - [PATCH v1 3/3] misc: fastrpc: Skip reference for DMA handles

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Message-ID: <20240822105933.2644945-4-quic_ekangupt@quicinc.com>
Date: Thu, 22 Aug 2024 16:29:33 +0530
From: Ekansh Gupta <quic_ekangupt@...cinc.com>
To: <srinivas.kandagatla@...aro.org>, <linux-arm-msm@...r.kernel.org>
CC: <gregkh@...uxfoundation.org>, <quic_bkumar@...cinc.com>,
        <linux-kernel@...r.kernel.org>, <quic_chennak@...cinc.com>,
        <dri-devel@...ts.freedesktop.org>, <arnd@...db.de>,
        stable
	<stable@...nel.org>
Subject: [PATCH v1 3/3] misc: fastrpc: Skip reference for DMA handles

If multiple dma handles are passed with same fd over a remote call
the kernel driver takes a reference and expects that put for the
map will be called as many times to free the map. But DSP only
updates the fd one time in the fd list when the DSP refcount
goes to zero and hence kernel make put call only once for the
fd. This can cause SMMU fault issue as the same fd can be used
in future for some other call.

Fixes: 35a82b87135d ("misc: fastrpc: Add dma handle implementation")
Cc: stable <stable@...nel.org>
Signed-off-by: Ekansh Gupta <quic_ekangupt@...cinc.com>
---
 drivers/misc/fastrpc.c | 13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
index ebe828770a8d..ad56e918e1f8 100644
--- a/drivers/misc/fastrpc.c
+++ b/drivers/misc/fastrpc.c
@@ -755,7 +755,7 @@ static const struct dma_buf_ops fastrpc_dma_buf_ops = {
 
 static int fastrpc_map_create(struct fastrpc_user *fl, int fd,
 				u64 va, u64 len, u32 attr,
-				struct fastrpc_map **ppmap)
+				struct fastrpc_map **ppmap, bool take_ref)
 {
 	struct fastrpc_session_ctx *sess = fl->sctx;
 	struct fastrpc_map *map = NULL;
@@ -763,7 +763,7 @@ static int fastrpc_map_create(struct fastrpc_user *fl, int fd,
 	struct scatterlist *sgl = NULL;
 	int err = 0, sgl_index = 0;
 
-	if (!fastrpc_map_lookup(fl, fd, va, len, ppmap, true))
+	if (!fastrpc_map_lookup(fl, fd, va, len, ppmap, take_ref))
 		return 0;
 
 	map = kzalloc(sizeof(*map), GFP_KERNEL);
@@ -917,14 +917,17 @@ static int fastrpc_create_maps(struct fastrpc_invoke_ctx *ctx)
 	int i, err;
 
 	for (i = 0; i < ctx->nscalars; ++i) {
+		bool take_ref = true;
 
 		if (ctx->args[i].fd == 0 || ctx->args[i].fd == -1 ||
 		    ctx->args[i].length == 0)
 			continue;
 
+		if (i >= ctx->nbufs)
+			take_ref = false;
 		err = fastrpc_map_create(ctx->fl, ctx->args[i].fd,
 				(u64)ctx->args[i].ptr, ctx->args[i].length,
-				ctx->args[i].attr, &ctx->maps[i]);
+				ctx->args[i].attr, &ctx->maps[i], take_ref);
 		if (err) {
 			dev_err(dev, "Error Creating map %d\n", err);
 			return -EINVAL;
@@ -1417,7 +1420,7 @@ static int fastrpc_init_create_process(struct fastrpc_user *fl,
 
 	if (init.filelen && init.filefd) {
 		err = fastrpc_map_create(fl, init.filefd, init.file,
-				init.filelen, 0, &map);
+				init.filelen, 0, &map, true);
 		if (err)
 			goto err;
 	}
@@ -2040,7 +2043,7 @@ static int fastrpc_req_mem_map(struct fastrpc_user *fl, char __user *argp)
 
 	/* create SMMU mapping */
 	err = fastrpc_map_create(fl, req.fd, req.vaddrin, req.length,
-			0, &map);
+			0, &map, true);
 	if (err) {
 		dev_err(dev, "failed to map buffer, fd = %d\n", req.fd);
 		return err;
-- 
2.34.1