linux-kernel - Re: [PATCH v2 1/1] initrd: move initrd_start calculate within linear mapping range check

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Date:   Mon, 1 Apr 2019 22:59:53 +0800
From:   pierre kuo <vichy.kuo@...il.com>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     Steven Price <steven.price@....com>,
        Will Deacon <will.deacon@....com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Florian Fainelli <f.fainelli@...il.com>
Subject: Re: [PATCH v2 1/1] initrd: move initrd_start calculate within linear
 mapping range check

hi Catalin:

> > With CONFIG_RANDOMIZE_BASE we can get a further change to memstart_addr
> > after the place where you moved the initrd_{start,end} setting, which
> > would result in a different value for __phys_to_virt(phys_initrd_start).
>
> I found what you mean, since __phys_to_virt will use PHYS_OFFSET
> (memstart_addr) for calculating.
> How about moving CONFIG_RANDOMIZE_BASE part of code ahead of
> CONFIG_BLK_DEV_INITRD checking?
>
> That means below (d) moving ahead of (c)
> prvious:
> if (memstart_addr + linear_region_size < memblock_end_of_DRAM()) {} ---(a)
> if (memory_limit != PHYS_ADDR_MAX) {}            ---(b)
> if (IS_ENABLED(CONFIG_BLK_DEV_INITRD) && phys_initrd_size) {} ---(c)
> if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {} ---(d)
>
> now:
> if (memstart_addr + linear_region_size < memblock_end_of_DRAM()) { ---(a)
> if (memory_limit != PHYS_ADDR_MAX) {}              ----------------(b)
> if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {}  --------------(d)
> if (IS_ENABLED(CONFIG_BLK_DEV_INITRD) && phys_initrd_size) {}  ---(c)
>

After tracing the kernel code,
is it even possible to move CONFIG_RANDOMIZE_BASE part of code ahead
of memory_limit?

that mean the flow may look like below:
now2:
if (memstart_addr + linear_region_size < memblock_end_of_DRAM()) {} ---(a)
if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {} ---(d)
if (memory_limit != PHYS_ADDR_MAX) {}            ---(b)
if (IS_ENABLED(CONFIG_BLK_DEV_INITRD) && phys_initrd_size) {} ---(c)

in (b), the result of __pa_symbol(_text), memory_limit,
memblock_mem_limit_remove_map and  memblock_add
are not depended on memsart_addr.
So the now2 flow can grouping modification of memstart_address, put
(a) and (d) together.

Sincerely Appreciate your comment.