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Message-ID: <2025112854-septum-asleep-8c35@gregkh>
Date: Fri, 28 Nov 2025 16:32:12 +0100
From: Greg KH <gregkh@...uxfoundation.org>
To: Ekansh Gupta <ekansh.gupta@....qualcomm.com>
Cc: srini@...nel.org, linux-arm-msm@...r.kernel.org,
quic_bkumar@...cinc.com, linux-kernel@...r.kernel.org,
quic_chennak@...cinc.com, dri-devel@...ts.freedesktop.org,
arnd@...db.de, dmitry.baryshkov@....qualcomm.com
Subject: Re: [PATCH v2 2/2] misc: fastrpc: Support mapping
userspace-allocated buffers
On Fri, Nov 28, 2025 at 04:04:28PM +0530, Ekansh Gupta wrote:
> Currently, FastRPC only supports mapping buffers allocated by the
> kernel. This limits flexibility for applications that allocate memory
> in userspace using rpcmem or DMABUF and need to share it with the DSP.
> Add support for mapping and unmapping userspace-allocated buffers to
> the DSP through SMMU. This includes handling map requests for rpcmem
> and DMABUF-backed memory and providing corresponding unmap
> functionality.
>
> Signed-off-by: Ekansh Gupta <ekansh.gupta@....qualcomm.com>
> ---
> drivers/misc/fastrpc.c | 96 +++++++++++++++++++++++++++++++++++++-----
> 1 file changed, 85 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
> index 9bf76e224852..feba79913763 100644
> --- a/drivers/misc/fastrpc.c
> +++ b/drivers/misc/fastrpc.c
> @@ -1854,8 +1854,10 @@ static int fastrpc_req_munmap_impl(struct fastrpc_user *fl, struct fastrpc_buf *
> static int fastrpc_req_munmap(struct fastrpc_user *fl, char __user *argp)
> {
> struct fastrpc_buf *buf = NULL, *iter, *b;
> + struct fastrpc_map *map = NULL, *iterm, *m;
> struct fastrpc_req_munmap req;
> struct device *dev = fl->sctx->dev;
> + int err;
>
> if (copy_from_user(&req, argp, sizeof(req)))
> return -EFAULT;
> @@ -1869,13 +1871,41 @@ static int fastrpc_req_munmap(struct fastrpc_user *fl, char __user *argp)
> }
> spin_unlock(&fl->lock);
>
> - if (!buf) {
> - dev_err(dev, "mmap\t\tpt 0x%09llx [len 0x%08llx] not in list\n",
> + if (buf) {
> + err = fastrpc_req_munmap_impl(fl, buf);
> + if (err) {
> + spin_lock(&fl->lock);
> + list_add_tail(&buf->node, &fl->mmaps);
> + spin_unlock(&fl->lock);
> + }
> + return err;
> + }
> +
> + spin_lock(&fl->lock);
> + list_for_each_entry_safe(iterm, m, &fl->maps, node) {
> + if (iterm->raddr == req.vaddrout) {
> + map = iterm;
> + list_del(&iterm->node);
> + break;
> + }
> + }
> + spin_unlock(&fl->lock);
> + if (!map) {
> + dev_dbg(dev, "buffer/map not found addr 0x%09llx, len 0x%08llx\n",
> req.vaddrout, req.size);
Never print out kernel pointers "raw" like this, use the real %p tags
instead. Odd that the current code does this, that is not good and is
probably a "information leak" somehow.
Can you fix that up first so it can be backported properly?
> return -EINVAL;
> }
>
> - return fastrpc_req_munmap_impl(fl, buf);
> + err = fastrpc_req_munmap_dsp(fl, map->raddr, map->size);
> + if (err) {
> + dev_dbg(dev, "unmmap\tpt fd = %d, 0x%09llx error\n", map->fd, map->raddr);
Same here. Also, no need for a \t in a kernel log message.
> + spin_lock(&fl->lock);
> + list_add_tail(&map->node, &fl->maps);
> + spin_unlock(&fl->lock);
> + } else {
> + fastrpc_map_put(map);
> + }
> + return err;
> }
>
> static int fastrpc_req_map_dsp(struct fastrpc_user *fl, u64 phys,
> @@ -1989,25 +2019,69 @@ static int fastrpc_req_buf_alloc(struct fastrpc_user *fl,
> return err;
> }
>
> -static int fastrpc_req_mmap(struct fastrpc_user *fl, char __user *argp)
> +static int fastrpc_req_map_create(struct fastrpc_user *fl,
> + struct fastrpc_req_mmap req,
> + char __user *argp)
> {
> - struct fastrpc_req_mmap req;
> + struct fastrpc_map *map = NULL;
> + struct device *dev = fl->sctx->dev;
> + u64 raddr = 0;
> int err;
>
> - if (copy_from_user(&req, argp, sizeof(req)))
> - return -EFAULT;
> + err = fastrpc_map_create(fl, req.fd, req.size, 0, &map);
> + if (err) {
> + dev_err(dev, "failed to map buffer, fd = %d\n", req.fd);
> + return err;
> + }
>
> - if (req.flags != ADSP_MMAP_ADD_PAGES && req.flags != ADSP_MMAP_REMOTE_HEAP_ADDR) {
> - dev_err(fl->sctx->dev, "flag not supported 0x%x\n", req.flags);
> + err = fastrpc_req_map_dsp(fl, map->phys, map->size, req.flags,
> + req.vaddrin, &raddr);
> + if (err)
> + goto err_invoke;
>
> - return -EINVAL;
> + /* update the buffer to be able to deallocate the memory on the DSP */
> + map->raddr = (u64)raddr;
> +
> + /* let the client know the address to use */
> + req.vaddrout = raddr;
> + dev_dbg(dev, "mmap\t\tpt 0x%09llx OK [len 0x%08llx]\n",
> + map->raddr, map->size);
> +
> + if (copy_to_user((void __user *)argp, &req, sizeof(req))) {
argp is already a user pointer, no need to cast it again, right?
> + err = -EFAULT;
> + goto err_copy;
> }
>
> - err = fastrpc_req_buf_alloc(fl, req, argp);
> + return 0;
> +err_copy:
> + fastrpc_req_munmap_dsp(fl, map->raddr, map->size);
> +err_invoke:
> + fastrpc_map_put(map);
>
> return err;
> }
>
> +static int fastrpc_req_mmap(struct fastrpc_user *fl, char __user *argp)
> +{
> + struct fastrpc_req_mmap req;
> + int err;
> +
> + if (copy_from_user(&req, argp, sizeof(req)))
> + return -EFAULT;
> +
> + if ((req.flags == ADSP_MMAP_ADD_PAGES ||
> + req.flags == ADSP_MMAP_REMOTE_HEAP_ADDR)) {
> + err = fastrpc_req_buf_alloc(fl, req, argp);
> + if (err)
> + return err;
> + } else {
> + err = fastrpc_req_map_create(fl, req, argp);
You changed the logic here from what used to happen if req.flags was not
set to those two values. Are you _sure_ you mean to do that? If so,
how does userspace know? Why don't you have a new flag for the new
type of memory you want to map?
thanks,
greg k-h
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