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

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Message-ID: <20190403172429.GE17500@fuggles.cambridge.arm.com>
Date:   Wed, 3 Apr 2019 18:24:29 +0100
From:   Will Deacon <will.deacon@....com>
To:     pierre kuo <vichy.kuo@...il.com>
Cc:     Catalin Marinas <catalin.marinas@....com>,
        Steven Price <steven.price@....com>,
        linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Florian Fainelli <f.fainelli@...il.com>,
        ard.biesheuvel@...aro.org
Subject: Re: [PATCH v2 1/1] initrd: move initrd_start calculate within linear
 mapping range check

On Thu, Apr 04, 2019 at 12:44:25AM +0800, pierre kuo wrote:
> > 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.

Maybe, but I don't think we've seen a patch which accomplishes that. I think
I'll go ahead and commit the basic one-liner, then we can always improve it
afterwards if somebody sends a patch. It's not like this is a fastpath.

Will