Re: [PATCH] dmaengine: mv_xor: protect MBUS window access with a spinlock

[Frank Li <Frank.li@oss.nxp.com>]

On Wed, Sep 16, 2026 at 11:26:08AM -0700, Rosen Penev wrote:
> mv_xor_add_io_win() reads and writes shared MBUS window registers
> and updates the shared win_start/win_end arrays in mv_xor_device.
> Multiple DMA channels can call this function concurrently via
> mv_xor_prep_dma_xor(), leading to races where two threads can
> select the same free window slot, corrupt the registers, or produce
> inconsistent cached state.
>
> Add a spinlock to struct mv_xor_device and hold it across the
> register read-modify-write and cache update in mv_xor_add_io_win().
>
> Fixes: 77ff7a706f01 ("mv_xor: Add support for IO (PCIe) src/dst areas")
> Assisted-by: LLM
> Signed-off-by: Rosen Penev <rosenp@gmail.com>
> ---
>  drivers/dma/mv_xor.c | 15 +++++++++++++--
>  drivers/dma/mv_xor.h |  1 +
>  2 files changed, 14 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/dma/mv_xor.c b/drivers/dma/mv_xor.c
> index 0de2b1ad5c30..e7c6ec54ce25 100644
> --- a/drivers/dma/mv_xor.c
> +++ b/drivers/dma/mv_xor.c
> @@ -497,11 +497,14 @@ static int mv_xor_add_io_win(struct mv_xor_chan *mv_chan, u32 addr)
>  	u8 target, attr;
>  	int ret;
>  	int i;
> +	unsigned long flags;
>
>  	/* Nothing needs to get done for the Armada 3700 */
>  	if (xordev->xor_type == XOR_ARMADA_37XX)
>  		return 0;
>
> +	spin_lock_irqsave(&xordev->win_lock, flags);
> +

use auto clean up guard()

Frank
>  	/*
>  	 * Loop over the cached windows to check, if the requested area
>  	 * is already mapped. If this the case, nothing needs to be done
> @@ -511,6 +514,7 @@ static int mv_xor_add_io_win(struct mv_xor_chan *mv_chan, u32 addr)
>  		if (addr >= xordev->win_start[i] &&
>  		    addr <= xordev->win_end[i]) {
>  			/* Window is already mapped */
> +			spin_unlock_irqrestore(&xordev->win_lock, flags);
>  			return 0;
>  		}
>  	}
> @@ -521,8 +525,10 @@ static int mv_xor_add_io_win(struct mv_xor_chan *mv_chan, u32 addr)
>
>  	/* If no IO window is found that addr has to be located in SDRAM */
>  	ret = mvebu_mbus_get_io_win_info(addr, &size, &target, &attr);
> -	if (ret < 0)
> +	if (ret < 0) {
> +		spin_unlock_irqrestore(&xordev->win_lock, flags);
>  		return 0;
> +	}
>
>  	/*
>  	 * Mask the base addr 'addr' according to 'size' read back from the
> @@ -540,8 +546,10 @@ static int mv_xor_add_io_win(struct mv_xor_chan *mv_chan, u32 addr)
>
>  	/* Set 'i' to the first free window to write the new values to */
>  	i = ffs(~win_enable) - 1;
> -	if (i >= WINDOW_COUNT)
> +	if (i >= WINDOW_COUNT) {
> +		spin_unlock_irqrestore(&xordev->win_lock, flags);
>  		return -ENOMEM;
> +	}
>
>  	writel((addr & 0xffff0000) | (attr << 8) | target,
>  	       base + WINDOW_BASE(i));
> @@ -556,6 +564,8 @@ static int mv_xor_add_io_win(struct mv_xor_chan *mv_chan, u32 addr)
>  	writel(win_enable, base + WINDOW_BAR_ENABLE(0));
>  	writel(win_enable, base + WINDOW_BAR_ENABLE(1));
>
> +	spin_unlock_irqrestore(&xordev->win_lock, flags);
> +
>  	return 0;
>  }
>
> @@ -1353,6 +1363,7 @@ static int mv_xor_probe(struct platform_device *pdev)
>
>  	platform_set_drvdata(pdev, xordev);
>
> +	spin_lock_init(&xordev->win_lock);
>
>  	/*
>  	 * We need to know which type of XOR device we use before
> diff --git a/drivers/dma/mv_xor.h b/drivers/dma/mv_xor.h
> index c87cefd38a07..034db4d0bfb1 100644
> --- a/drivers/dma/mv_xor.h
> +++ b/drivers/dma/mv_xor.h
> @@ -80,6 +80,7 @@ struct mv_xor_device {
>  	struct clk	     *clk;
>  	struct mv_xor_chan   *channels[MV_XOR_MAX_CHANNELS];
>  	int		     xor_type;
> +	spinlock_t	     win_lock;
>
>  	u32                  win_start[WINDOW_COUNT];
>  	u32                  win_end[WINDOW_COUNT];
> --
> 2.55.0
>