[PATCH backport to 5.4 and below 1/1] serial: 8250: Flush DMA Rx on RLSI

[PATCH backport to 5.4 and below 1/1] serial: 8250: Flush DMA Rx on RLSI

[Ilpo Järvinen]

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commit 1980860e0c8299316cddaf0992dd9e1258ec9d88 upstream.

Returning true from handle_rx_dma() without flushing DMA first creates
a data ordering hazard. If DMA Rx has handled any character at the
point when RLSI occurs, the non-DMA path handles any pending characters
jumping them ahead of those characters that are pending under DMA.

Fixes: 75df022b5f89 ("serial: 8250_dma: Fix RX handling")
Cc: <stable@vger.kernel.org>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20221108121952.5497-5-ilpo.jarvinen@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/tty/serial/8250/8250_port.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index 97a64bc79350..b47335dfae16 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -1824,10 +1824,9 @@ static bool handle_rx_dma(struct uart_8250_port *up, unsigned int iir)
 		if (!up->dma->rx_running)
 			break;
 		fallthrough;
+	case UART_IIR_RLSI:
 	case UART_IIR_RX_TIMEOUT:
 		serial8250_rx_dma_flush(up);
-		/* fall-through */
-	case UART_IIR_RLSI:
 		return true;
 	}
 	return up->dma->rx_dma(up);
-- 
2.30.2

Re: [PATCH backport to 5.4 and below 1/1] serial: 8250: Flush DMA Rx on RLSI

[Greg Kroah-Hartman]

On Mon, Nov 21, 2022 at 02:49:25PM +0200, Ilpo Järvinen wrote:
> commit 1980860e0c8299316cddaf0992dd9e1258ec9d88 upstream.
> 
> Returning true from handle_rx_dma() without flushing DMA first creates
> a data ordering hazard. If DMA Rx has handled any character at the
> point when RLSI occurs, the non-DMA path handles any pending characters
> jumping them ahead of those characters that are pending under DMA.
> 
> Fixes: 75df022b5f89 ("serial: 8250_dma: Fix RX handling")
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> Link: https://lore.kernel.org/r/20221108121952.5497-5-ilpo.jarvinen@linux.intel.com
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
>  drivers/tty/serial/8250/8250_port.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)

Applied to 5.4.y only.  Fails to apply to 4.9.y, 4.14.y, or 4.19.y :(

Re: [PATCH backport to 4.19 and below 1/1] serial: 8250: Flush DMA Rx on RLSI

[Ilpo Järvinen]

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commit 1980860e0c8299316cddaf0992dd9e1258ec9d88 upstream.

Returning true from handle_rx_dma() without flushing DMA first creates
a data ordering hazard. If DMA Rx has handled any character at the
point when RLSI occurs, the non-DMA path handles any pending characters
jumping them ahead of those characters that are pending under DMA.

Fixes: 75df022b5f89 ("serial: 8250_dma: Fix RX handling")
Cc: <stable@vger.kernel.org>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20221108121952.5497-5-ilpo.jarvinen@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 drivers/tty/serial/8250/8250_port.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
index cab3a74281ef..8aee43fe488a 100644
--- a/drivers/tty/serial/8250/8250_port.c
+++ b/drivers/tty/serial/8250/8250_port.c
@@ -1802,10 +1802,9 @@ static bool handle_rx_dma(struct uart_8250_port *up, unsigned int iir)
 		if (!up->dma->rx_running)
 			break;
 		/* fall-through */
+	case UART_IIR_RLSI:
 	case UART_IIR_RX_TIMEOUT:
 		serial8250_rx_dma_flush(up);
-		/* fall-through */
-	case UART_IIR_RLSI:
 		return true;
 	}
 	return up->dma->rx_dma(up);
-- 
2.30.2

Re: [PATCH backport to 4.19 and below 1/1] serial: 8250: Flush DMA Rx on RLSI

[Greg Kroah-Hartman]

On Tue, Nov 22, 2022 at 03:14:10PM +0200, Ilpo Järvinen wrote:
> commit 1980860e0c8299316cddaf0992dd9e1258ec9d88 upstream.
> 
> Returning true from handle_rx_dma() without flushing DMA first creates
> a data ordering hazard. If DMA Rx has handled any character at the
> point when RLSI occurs, the non-DMA path handles any pending characters
> jumping them ahead of those characters that are pending under DMA.
> 
> Fixes: 75df022b5f89 ("serial: 8250_dma: Fix RX handling")
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
> Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
> Link: https://lore.kernel.org/r/20221108121952.5497-5-ilpo.jarvinen@linux.intel.com
> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ---
>  drivers/tty/serial/8250/8250_port.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/tty/serial/8250/8250_port.c b/drivers/tty/serial/8250/8250_port.c
> index cab3a74281ef..8aee43fe488a 100644
> --- a/drivers/tty/serial/8250/8250_port.c
> +++ b/drivers/tty/serial/8250/8250_port.c
> @@ -1802,10 +1802,9 @@ static bool handle_rx_dma(struct uart_8250_port *up, unsigned int iir)
>  		if (!up->dma->rx_running)
>  			break;
>  		/* fall-through */
> +	case UART_IIR_RLSI:
>  	case UART_IIR_RX_TIMEOUT:
>  		serial8250_rx_dma_flush(up);
> -		/* fall-through */
> -	case UART_IIR_RLSI:
>  		return true;
>  	}
>  	return up->dma->rx_dma(up);
> -- 
> 2.30.2


Now queued up, thanks.

greg k-h