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Subject: Re: [PATCH v2] kernel/dma: Fix panic caused by passing swiotlb to
 command line
To:     <konrad@darnok.org>, <konrad.wilk@oracle.com>, <hch@lst.de>,
        <m.szyprowski@samsung.com>, <robin.murphy@arm.com>,
        <iommu@lists.linux-foundation.org>, <linux-kernel@vger.kernel.org>
References: <1543832571-121638-1-git-send-email-zhe.he@windriver.com>
From:   He Zhe <zhe.he@windriver.com>
Message-ID: <b35907a9-4d30-493b-3839-731b10d71c63@windriver.com>
Date:   Mon, 7 Jan 2019 16:46:51 +0800
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Kindly ping.

Zhe

On 12/3/18 6:22 PM, zhe.he@windriver.com wrote:
> From: He Zhe <zhe.he@windriver.com>
>
> setup_io_tlb_npages does not check input argument before passing it
> to isdigit. The argument would be a NULL pointer if "swiotlb", without
> its value, is set in command line and thus causes the following panic.
>
> PANIC: early exception 0xe3 IP 10:ffffffffbb9b8e9f error 0 cr2 0x0
> [    0.000000] CPU: 0 PID: 0 Comm: swapper Not tainted 4.19.0-rc3-yocto-standard+ #9
> [    0.000000] RIP: 0010:setup_io_tlb_npages+0xf/0x95
> ...
> [    0.000000] Call Trace:
> [    0.000000]  do_early_param+0x57/0x8e
> [    0.000000]  parse_args+0x208/0x320
> [    0.000000]  ? rdinit_setup+0x30/0x30
> [    0.000000]  parse_early_options+0x29/0x2d
> [    0.000000]  ? rdinit_setup+0x30/0x30
> [    0.000000]  parse_early_param+0x36/0x4d
> [    0.000000]  setup_arch+0x336/0x99e
> [    0.000000]  start_kernel+0x6f/0x4e6
> [    0.000000]  x86_64_start_reservations+0x24/0x26
> [    0.000000]  x86_64_start_kernel+0x6f/0x72
> [    0.000000]  secondary_startup_64+0xa4/0xb0
>
> This patch adds a check to prevent the panic and sets it for 4MB by default.
>
> Signed-off-by: He Zhe <zhe.he@windriver.com>
> Cc: stable@vger.kernel.org
> Cc: konrad.wilk@oracle.com
> Cc: hch@lst.de
> Cc: m.szyprowski@samsung.com
> Cc: robin.murphy@arm.com
>
> Signed-off-by: He Zhe <zhe.he@windriver.com>
> ---
> v2: Set swiotlb for 4MB by default
>
>  kernel/dma/swiotlb.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
>
> diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
> index 045930e..0e18cd4 100644
> --- a/kernel/dma/swiotlb.c
> +++ b/kernel/dma/swiotlb.c
> @@ -58,6 +58,9 @@
>   */
>  #define IO_TLB_MIN_SLABS ((1<<20) >> IO_TLB_SHIFT)
>  
> +#define IO_TLB_DEFAULT_MB 4
> +#define IO_TLB_DEFAULT_SLABS ((IO_TLB_DEFAULT_MB<<20) >> IO_TLB_SHIFT)
> +
>  enum swiotlb_force swiotlb_force;
>  
>  /*
> @@ -103,6 +106,14 @@ static int late_alloc;
>  static int __init
>  setup_io_tlb_npages(char *str)
>  {
> +	if (!str) {
> +		pr_err("No value provided for swiotlb, "
> +		       "set it to %d slabs for %dMB by default.\n",
> +		       IO_TLB_DEFAULT_SLABS, IO_TLB_DEFAULT_MB);
> +		io_tlb_nslabs = IO_TLB_DEFAULT_SLABS;
> +		return 0;
> +	}
> +
>  	if (isdigit(*str)) {
>  		io_tlb_nslabs = simple_strtoul(str, &str, 0);
>  		/* avoid tail segment of size < IO_TLB_SEGSIZE */