linux-kernel - Re: [PATCH v2] MIPS: fix incorrect mem=X@Y handling

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Date:   Tue, 23 Jan 2018 14:17:57 +0000
From:   James Hogan <jhogan@...nel.org>
To:     Mathieu Malaterre <malat@...ian.org>
Cc:     Marcin Nowakowski <marcin.nowakowski@...s.com>,
        "# v4 . 11" <stable@...r.kernel.org>,
        Ralf Baechle <ralf@...ux-mips.org>, linux-mips@...ux-mips.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] MIPS: fix incorrect mem=X@Y handling

On Thu, Dec 21, 2017 at 10:00:59PM +0100, Mathieu Malaterre wrote:
> From: Marcin Nowakowski <marcin.nowakowski@...s.com>
> 
> Change 73fbc1eba7ff added a fix to ensure that the memory range between

Please refer to commits with e.g. commit 73fbc1eba7ff ("MIPS: fix
mem=X@Y commandline processing").

> PHYS_OFFSET and low memory address specified by mem= cmdline argument is
> not later processed by free_all_bootmem.
> This change was incorrect for systems where the commandline specifies
> more than 1 mem argument, as it will cause all memory between
> PHYS_OFFSET and each of the memory offsets to be marked as reserved,
> which results in parts of the RAM marked as reserved (Creator CI20's
> u-boot has a default commandline argument 'mem=256M@0x0
> mem=768M@...0000000').
> 
> Change the behaviour to ensure that only the range between PHYS_OFFSET
> and the lowest start address of the memories is marked as protected.
> 
> This change also ensures that the range is marked protected even if it's
> only defined through the devicetree and not only via commandline
> arguments.
> 
> Reported-by: Mathieu Malaterre <mathieu.malaterre@...il.com>
> Signed-off-by: Marcin Nowakowski <marcin.nowakowski@...s.com>
> Fixes: 73fbc1eba7ff ("MIPS: fix mem=X@Y commandline processing")
> Cc: <stable@...r.kernel.org> # v4.11

I'm guessing that should technically be v4.11+

> ---
> v2: Use updated email adress, add tag for stable.
>  arch/mips/kernel/setup.c | 19 ++++++++++++++++---
>  1 file changed, 16 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/mips/kernel/setup.c b/arch/mips/kernel/setup.c
> index 702c678de116..f19d61224c71 100644
> --- a/arch/mips/kernel/setup.c
> +++ b/arch/mips/kernel/setup.c
> @@ -375,6 +375,7 @@ static void __init bootmem_init(void)
>  	unsigned long reserved_end;
>  	unsigned long mapstart = ~0UL;
>  	unsigned long bootmap_size;
> +	phys_addr_t ramstart = ~0UL;

Although practically it might not matter, technically phys_addr_t may be
64-bits (CONFIG_PHYS_ADDR_T_64BIT) even on a 32-bit kernels, in which
case ~0UL may not be sufficiently large.

Maybe that should be ~(phys_addr_t)0, or perhaps (phys_addr_t)ULLONG_MAX
to match add_memory_region().

>  	bool bootmap_valid = false;
>  	int i;
>  
> @@ -395,6 +396,21 @@ static void __init bootmem_init(void)
>  	max_low_pfn = 0;
>  
>  	/*
> +	 * Reserve any memory between the start of RAM and PHYS_OFFSET
> +	 */
> +	for (i = 0; i < boot_mem_map.nr_map; i++) {
> +		if (boot_mem_map.map[i].type != BOOT_MEM_RAM)
> +			continue;
> +
> +		ramstart = min(ramstart, boot_mem_map.map[i].addr);

Is it worth incorporating this into the existing loop below ...

> +	}
> +
> +	if (ramstart > PHYS_OFFSET)
> +		add_memory_region(PHYS_OFFSET, ramstart - PHYS_OFFSET,
> +				  BOOT_MEM_RESERVED);

... and this then placed below that loop?

Otherwise I can't find fault with this patch, though i'm not intimately
familiar with bootmem.

Cheers
James

> +
> +
> +	/*
>  	 * Find the highest page frame number we have available.
>  	 */
>  	for (i = 0; i < boot_mem_map.nr_map; i++) {
> @@ -664,9 +680,6 @@ static int __init early_parse_mem(char *p)
>  
>  	add_memory_region(start, size, BOOT_MEM_RAM);
>  
> -	if (start && start > PHYS_OFFSET)
> -		add_memory_region(PHYS_OFFSET, start - PHYS_OFFSET,
> -				BOOT_MEM_RESERVED);
>  	return 0;
>  }
>  early_param("mem", early_parse_mem);
> -- 
> 2.11.0
> 

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