linux-kernel - Re: [PATCH v1 2/3] misc: fastrpc: Update context ID mask for polling mode support

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: <dqkd4jxzrn4l6notk45udbapcan7icph5lpaoccgenm53kt4me@n7sv2rnf37im>
Date: Tue, 2 Sep 2025 07:12:21 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@....qualcomm.com>
To: Ekansh Gupta <ekansh.gupta@....qualcomm.com>
Cc: 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 v1 2/3] misc: fastrpc: Update context ID mask for polling
 mode support

On Mon, Sep 01, 2025 at 11:03:35AM +0530, Ekansh Gupta wrote:
> Current fastrpc message context uses a 12-bit mask where the upper
> 8 bits are context ID from idr_alloc_cyclic and the lower 4 bits
> represent PD type. This design works for normal fastrpc calls but

FastRPC (here and in several other places).

> doesn't work as expected for polling mode. To enable polling mode
> support from DSP(DSP writes to poll memory), DSP expects a 16-bit
> context where the upper 8 bits are context ID, the lower 4 bits are
> PD type and the 5th bit from the end denotes async mode(not yet
> upstreamed). If this bit is set, DSP disables polling. With the
> current design, odd context IDs set this bit, causing DSP to skip
> poll memory updates.

This looks like a description of a bugfix. In such a case, move it to
the start of the series, add necessary tatgs and change commit message
accordingly.

> Update the context mask to ensure a hole
> which won't get populated, ensuring polling mode works as expected.
> 
> Signed-off-by: Ekansh Gupta <ekansh.gupta@....qualcomm.com>
> ---
>  drivers/misc/fastrpc.c | 8 ++++----
>  1 file changed, 4 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/misc/fastrpc.c b/drivers/misc/fastrpc.c
> index 0991ac487192..57e118de6e4a 100644
> --- a/drivers/misc/fastrpc.c
> +++ b/drivers/misc/fastrpc.c
> @@ -37,7 +37,7 @@
>  #define FASTRPC_CTX_MAX (256)
>  #define FASTRPC_INIT_HANDLE	1
>  #define FASTRPC_DSP_UTILITIES_HANDLE	2
> -#define FASTRPC_CTXID_MASK (0xFF0)
> +#define FASTRPC_CTXID_MASK (0xFF00)
>  #define INIT_FILELEN_MAX (2 * 1024 * 1024)
>  #define INIT_FILE_NAMELEN_MAX (128)
>  #define FASTRPC_DEVICE_NAME	"fastrpc"
> @@ -487,7 +487,7 @@ static void fastrpc_context_free(struct kref *ref)
>  		fastrpc_buf_free(ctx->buf);
>  
>  	spin_lock_irqsave(&cctx->lock, flags);
> -	idr_remove(&cctx->ctx_idr, ctx->ctxid >> 4);
> +	idr_remove(&cctx->ctx_idr, ctx->ctxid >> 8);

#define magic value

>  	spin_unlock_irqrestore(&cctx->lock, flags);
>  
>  	kfree(ctx->maps);
> @@ -623,7 +623,7 @@ static struct fastrpc_invoke_ctx *fastrpc_context_alloc(
>  		spin_unlock_irqrestore(&cctx->lock, flags);
>  		goto err_idr;
>  	}
> -	ctx->ctxid = ret << 4;
> +	ctx->ctxid = ret << 8;
>  	spin_unlock_irqrestore(&cctx->lock, flags);
>  
>  	kref_init(&ctx->refcount);
> @@ -2449,7 +2449,7 @@ static int fastrpc_rpmsg_callback(struct rpmsg_device *rpdev, void *data,
>  	if (len < sizeof(*rsp))
>  		return -EINVAL;
>  
> -	ctxid = ((rsp->ctx & FASTRPC_CTXID_MASK) >> 4);
> +	ctxid = ((rsp->ctx & FASTRPC_CTXID_MASK) >> 8);
>  
>  	spin_lock_irqsave(&cctx->lock, flags);
>  	ctx = idr_find(&cctx->ctx_idr, ctxid);
> -- 
> 2.34.1
> 

-- 
With best wishes
Dmitry