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

From: pierre kuo <vichy.kuo@gmail.com>
To: Will Deacon <will.deacon@arm.com>
Cc: Catalin Marinas <catalin.marinas@arm.com>,
	Steven Price <steven.price@arm.com>,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	Florian Fainelli <f.fainelli@gmail.com>,
	ard.biesheuvel@linaro.org
Subject: Re: [PATCH v2 1/1] initrd: move initrd_start calculate within linear mapping range check
Date: Thu, 4 Apr 2019 00:44:25 +0800	[thread overview]
Message-ID: <CAOVJa8EcjQO2GuojwBxfFG25+T-z6BR6ytZBdcV2W2XusyW08g@mail.gmail.com> (raw)
In-Reply-To: <20190401153810.GC6884@fuggles.cambridge.arm.com>

hi Will:
>
> [+Ard in case I'm missing something]
>
> On Mon, Apr 01, 2019 at 10:59:53PM +0800, pierre kuo wrote:
> > > > 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.
>
> I'm afraid that you've lost me with this.
welcome for ur kind suggestion ^^

>Why isn't it just as simple as
> the diff below?
> diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> index c29b17b520cd..ec3487c94b10 100644
> --- a/arch/arm64/mm/init.c
> +++ b/arch/arm64/mm/init.c
> @@ -377,7 +377,7 @@ void __init arm64_memblock_init(void)
>                          base + size > memblock_start_of_DRAM() +
>                                        linear_region_size,
>                         "initrd not fully accessible via the linear mapping -- please check your bootloader ...\n")) {
> -                       initrd_start = 0;
> +                       phys_initrd_size = 0;
>                 } else {
>                         memblock_remove(base, size); /* clear MEMBLOCK_ flags */
>                         memblock_add(base, size);

This patch will also fix the issue, but it still needs 2 "if
comparisions" for getting initrd_start/initrd_end.
By possible grouping modification of memstart_address, and put
initrd_start/initrd_end to be calculated only when linear mapping check
pass. Maybe (just if) can let the code be more concise.

Sincerely appreciate all of yours great comment.