linux-kernel - Re: [PATCH] of: Check for overlap in reserved memory regions

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Date:	Mon, 14 Sep 2015 14:21:04 -0500
From:	Rob Herring <robh@...nel.org>
To:	Mitchel Humpherys <mitchelh@...eaurora.org>
Cc:	Rob Herring <robh+dt@...nel.org>,
	Frank Rowand <frowand.list@...il.com>,
	Grant Likely <grant.likely@...aro.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] of: Check for overlap in reserved memory regions

On Fri, Sep 11, 2015 at 12:31 PM, Mitchel Humpherys
<mitchelh@...eaurora.org> wrote:
> Any overlap in the reserved memory regions (those specified in the
> reserved-memory DT node) is a bug.  These bugs might go undetected as
> long as the contested region isn't used simultaneously by multiple
> software agents, which makes such bugs hard to debug.  Fix this by
> printing a scary warning during boot if overlap is detected.
>
> Signed-off-by: Mitchel Humpherys <mitchelh@...eaurora.org>
> ---
>  drivers/of/of_reserved_mem.c | 45 +++++++++++++++++++++++++++++++++++++++++++-
>  1 file changed, 44 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/of/of_reserved_mem.c b/drivers/of/of_reserved_mem.c
> index 726ebe792813..5246d346cee0 100644
> --- a/drivers/of/of_reserved_mem.c
> +++ b/drivers/of/of_reserved_mem.c
> @@ -1,7 +1,7 @@
>  /*
>   * Device tree based initialization code for reserved memory.
>   *
> - * Copyright (c) 2013, The Linux Foundation. All Rights Reserved.
> + * Copyright (c) 2013, 2015 The Linux Foundation. All Rights Reserved.
>   * Copyright (c) 2013,2014 Samsung Electronics Co., Ltd.
>   *             http://www.samsung.com
>   * Author: Marek Szyprowski <m.szyprowski@...sung.com>
> @@ -20,9 +20,11 @@
>  #include <linux/mm.h>
>  #include <linux/sizes.h>
>  #include <linux/of_reserved_mem.h>
> +#include <linux/sort.h>
>
>  #define MAX_RESERVED_REGIONS   16
>  static struct reserved_mem reserved_mem[MAX_RESERVED_REGIONS];
> +static struct reserved_mem sorted_reserved_mem[MAX_RESERVED_REGIONS] __initdata;
>  static int reserved_mem_count;
>
>  #if defined(CONFIG_HAVE_MEMBLOCK)
> @@ -197,12 +199,53 @@ static int __init __reserved_mem_init_node(struct reserved_mem *rmem)
>         return -ENOENT;
>  }
>
> +static int __init __rmem_cmp(const void *a, const void *b)
> +{
> +       const struct reserved_mem *ra = a, *rb = b;
> +
> +       return ra->base - rb->base;
> +}
> +
> +static void __init __rmem_check_for_overlap(void)
> +{
> +       int i;
> +
> +       if (reserved_mem_count < 2)
> +               return;
> +
> +       memcpy(sorted_reserved_mem, reserved_mem, sizeof(sorted_reserved_mem));
> +       sort(sorted_reserved_mem, reserved_mem_count,
> +            sizeof(sorted_reserved_mem[0]), __rmem_cmp, NULL);

Why not just sort reserved_mem?

> +       for (i = 0; i < reserved_mem_count - 1; i++) {
> +               struct reserved_mem *this, *next;
> +
> +               this = &sorted_reserved_mem[i];
> +               next = &sorted_reserved_mem[i + 1];
> +               if (!(this->base && next->base))
> +                       continue;
> +               if (this->base + this->size > next->base) {
> +                       phys_addr_t this_end, next_end;
> +
> +                       this_end = this->base + this->size;
> +                       next_end = next->base + next->size;
> +                       WARN(1, "Reserved mem: OVERLAP DETECTED!\n");
> +                       pr_err("%s (%pa--%pa) overlaps with %s (%pa--%pa)\n",

This seems overly verbose having both WARN and pr_err. I'd combine
these. I don't think the stack trace from a WARN is too useful here
given it is the DT file that users will need to go look at.

> +                              this->name, &this->base, &this_end,
> +                              next->name, &next->base, &next_end);
> +               }
> +       }
> +}
> +
>  /**
>   * fdt_init_reserved_mem - allocate and init all saved reserved memory regions
>   */
>  void __init fdt_init_reserved_mem(void)
>  {
>         int i;
> +
> +       /* check for overlapping reserved regions */
> +       __rmem_check_for_overlap();
> +
>         for (i = 0; i < reserved_mem_count; i++) {
>                 struct reserved_mem *rmem = &reserved_mem[i];
>                 unsigned long node = rmem->fdt_node;
> --
> Qualcomm Innovation Center, Inc.
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
> a Linux Foundation Collaborative Project
>
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