linux-kernel - Re: [PATCH] of: Fix reserved-memory overlap detection

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Date:   Tue, 20 Oct 2020 09:17:27 -0500
From:   Rob Herring <robh+dt@...nel.org>
To:     Vincent Whitchurch <vincent.whitchurch@...s.com>
Cc:     Frank Rowand <frowand.list@...il.com>, kernel <kernel@...s.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] of: Fix reserved-memory overlap detection

On Tue, Oct 20, 2020 at 8:46 AM Vincent Whitchurch
<vincent.whitchurch@...s.com> wrote:
>
> On Tue, Oct 20, 2020 at 03:00:14PM +0200, Rob Herring wrote:
> > On Tue, Oct 20, 2020 at 2:36 AM Vincent Whitchurch
> > <vincent.whitchurch@...s.com> wrote:
> > >
> > > The reserved-memory overlap detection code fails to detect overlaps if
> > > either of the regions starts at address 0x0.  For some reason the code
> > > explicitly checks for and ignores such regions, but this check looks
> > > invalid.  Remove the check and fix this detection.
> >
> > Wouldn't 'base' be 0 for nodes that have a 'size' and no address? The
> > base in those cases isn't set until later when
> > __reserved_mem_alloc_size() is called.
>
> Ah, yes, I guess that's why the check was there.  I see that those
> entries have both a zero address and a zero size, so this seems to work:

Yes, I think it should work.

>
> diff --git a/arch/arm/boot/dts/vexpress-v2p-ca9.dts b/arch/arm/boot/dts/vexpress-v2p-ca9.dts
> index 623246f37448..6627e71c7283 100644
> --- a/arch/arm/boot/dts/vexpress-v2p-ca9.dts
> +++ b/arch/arm/boot/dts/vexpress-v2p-ca9.dts
> @@ -81,6 +81,18 @@ vram: vram@...00000 {
>                         reg = <0x4c000000 0x00800000>;
>                         no-map;
>                 };
> +
> +               foo@0 {
> +                       reg = <0x0 0x2000>;
> +               };
> +
> +               bar@...0 {
> +                       reg = <0x0 0x1000>;

0x1000 base?

> +               };
> +
> +               baz {
> +                       size = <0x1000>;
> +               };
>         };
>
>         clcd@...20000 {
> diff --git a/drivers/of/of_reserved_mem.c b/drivers/of/of_reserved_mem.c
> index 46b9371c8a33..fea9433d942a 100644
> --- a/drivers/of/of_reserved_mem.c
> +++ b/drivers/of/of_reserved_mem.c
> @@ -200,6 +200,16 @@ static int __init __rmem_cmp(const void *a, const void *b)
>         if (ra->base > rb->base)
>                 return 1;
>
> +       /*
> +        * Put the dynamic allocations (address == 0, size == 0) before static
> +        * allocations at address 0x0 so that overlap detection works
> +        * correctly.
> +        */
> +       if (ra->size < rb->size)
> +               return -1;
> +       if (ra->size > rb->size)
> +               return 1;
> +
>         return 0;
>  }
>
> @@ -212,13 +222,19 @@ static void __init __rmem_check_for_overlap(void)
>
>         sort(reserved_mem, reserved_mem_count, sizeof(reserved_mem[0]),
>              __rmem_cmp, NULL);
> +
> +       for (i = 0; i < reserved_mem_count - 1; i++) {
> +               struct reserved_mem *this = &reserved_mem[i];
> +
> +               pr_info("i %d base %x size %x\n", i, this->base, this->size);
> +       }
> +
>         for (i = 0; i < reserved_mem_count - 1; i++) {
>                 struct reserved_mem *this, *next;
>
>                 this = &reserved_mem[i];
>                 next = &reserved_mem[i + 1];
> -               if (!(this->base && next->base))
> -                       continue;
> +
>                 if (this->base + this->size > next->base) {
>                         phys_addr_t this_end, next_end;
>