linux-kernel - Re: [PATCH v3 4/4] misc: fastrpc: Skip reference for DMA handles

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Message-ID: <eyqm52g3oymidbylo2jp4uihp7luwhoet2sj5oxoz52bcsnhhx@vusta6qaws3t>
Date: Thu, 14 Aug 2025 10:03:43 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Ling Xu <quic_lxu5@...cinc.com>
Cc: srini@...nel.org, amahesh@....qualcomm.com, arnd@...db.de,
        gregkh@...uxfoundation.org, sumit.semwal@...aro.org,
        christian.koenig@....com, thierry.escande@...aro.org,
        quic_vgattupa@...cinc.com, quic_kuiw@...cinc.com,
        ekansh.gupta@....qualcomm.com, dri-devel@...ts.freedesktop.org,
        linux-arm-msm@...r.kernel.org, linux-media@...r.kernel.org,
        linaro-mm-sig@...ts.linaro.org, linux-kernel@...r.kernel.org,
        stable@...nel.org
Subject: Re: [PATCH v3 4/4] misc: fastrpc: Skip reference for DMA handles

On Thu, Aug 07, 2025 at 03:34:20PM +0530, Ling Xu wrote:
> 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@...nel.org
> Co-developed-by: Ekansh Gupta <ekansh.gupta@....qualcomm.com>
> Signed-off-by: Ekansh Gupta <ekansh.gupta@....qualcomm.com>
> Signed-off-by: Ling Xu <quic_lxu5@...cinc.com>
> ---
>  drivers/misc/fastrpc.c | 45 +++++++++++++++++++++++++-----------------
>  1 file changed, 27 insertions(+), 18 deletions(-)
> 

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>


-- 
With best wishes
Dmitry