linux-kernel - Re: [PATCH v3 3/3] misc: fastrpc: Support mapping userspace-allocated buffers

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CACSVV02ArZQYW0D66wCzcLoegAB+vUODDxfX4Vbt3xpBajRKYg@mail.gmail.com>
Date: Thu, 29 Jan 2026 14:11:12 -0800
From: Rob Clark <rob.clark@....qualcomm.com>
To: Ekansh Gupta <ekansh.gupta@....qualcomm.com>
Cc: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>, srini@...nel.org,
        linux-arm-msm@...r.kernel.org, gregkh@...uxfoundation.org,
        quic_bkumar@...cinc.com, linux-kernel@...r.kernel.org,
        quic_chennak@...cinc.com, dri-devel@...ts.freedesktop.org,
        arnd@...db.de
Subject: Re: [PATCH v3 3/3] misc: fastrpc: Support mapping userspace-allocated buffers

On Thu, Jan 29, 2026 at 2:39 AM Ekansh Gupta
<ekansh.gupta@....qualcomm.com> wrote:
>
>
>
> On 1/6/2026 8:21 AM, Dmitry Baryshkov wrote:
> > On Tue, Dec 30, 2025 at 04:32:25PM +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.
> > Hmm, for DMABUF we need _import_ support rather than support for mapping
> > of userspace-allocated buffers.
> >
> >> 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.
> > For me this definitely looks like a step back. For drm/accel we are
> > going to have GEM-managed buffers only. Why do we need to handle
> > userspace-allocated buffers here?
> That's correct, GEM-PRIME will handle it properly. Here, the reason to add this
> change is to enable routing of DSP logs to HLOS which is done by using a shared
> buffer between userspace process and DSP PD. The buffer can be allocated from
> both fastrpc driver's DMA-BUF or DMABUF heap(eg. system heap).
>
> So this shared buffer is getting mapped to both process's IOMMU device and DSP PD
> with this change.

So, a mmap'd dma-buf is not necessarily pinned.  Or even backed with
pages.  So you wouldn't want to try to map a userspace vaddr from a
dma-buf to the device.

But looking at the patch, this looks more like mapping an imported
dmabuf?  Presumably going thru dma_buf_map_attachment() somewhere in
the existing fastrpc code?

BR,
-R

> >
> >> Signed-off-by: Ekansh Gupta <ekansh.gupta@....qualcomm.com>
> >> ---
> >>  drivers/misc/fastrpc.c | 97 +++++++++++++++++++++++++++++++++++++-----
> >>  1 file changed, 86 insertions(+), 11 deletions(-)
> >>
> >> @@ -1989,25 +2020,69 @@ 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;
> >> +    }
> >> +
> >> +    err = fastrpc_req_map_dsp(fl, map->phys, map->size, req.flags,
> >> +                              req.vaddrin, &raddr);
> >> +    if (err)
> >> +            goto err_invoke;
> >>
> >> -    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);
> >> +    /* update the buffer to be able to deallocate the memory on the DSP */
> >> +    map->raddr = (u64)raddr;
> > Which type are you converting? And why?
> I'll drop this.
> >
> >>
> >> -            return -EINVAL;
> >> +    /* let the client know the address to use */
> >> +    req.vaddrout = raddr;
> >> +    dev_dbg(dev, "mmap OK: raddr=%p [len=0x%08llx]\n",
> >> +            (void *)(unsigned long)map->raddr, map->size);
> >> +
> >> +    if (copy_to_user(argp, &req, sizeof(req))) {
> >> +            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)) {
> > Side note: why are these flags not defined in the uABI header?
> Ack. These should be part of uABI. I'll create a separate patch for this.
> >
> >> +            err = fastrpc_req_buf_alloc(fl, req, argp);
> >> +            if (err)
> >> +                    return err;
>