Subject: [PATCH] arm64:mm Remove the redundant initrd memblock codes

From: [email-masked] (Dennis Chen)
Date: Tue, 5 Jul 2016 10:22:18 +0800

On Mon, Jul 04, 2016 at 12:33:05PM +0200, Ard Biesheuvel wrote:
> 
> > On 4 jul. 2016, at 06:53, Dennis Chen <[email-masked]> wrote:
> > 
> > The memory range between initrd_start and initrd_end was added to the memblock
> > twice unnecessarily in the same function before initrd memory range can be freed.
> > This patch merge those codes into one piece of block and add the initrd memory
> > range only once, also it makes the code clean and simple.
> > 
> 
> This is likely to break under KASLR (and I would recommend that you test with kaslr enabled when you propose changes to this code)
>
Hello Ard, I've tested it under KASLR on Juno board before proposing the changes,where the firmware provides the RNG protocol, it works well.
> 
> The randomization of memstart_addr needs to execute /after/ adding back the initrd, otherwise the chosen value of memstart_addr may push the initrd beyond the end of the linear area into the userland range.
>
Yes, I know the 'range' is depends on memblock_end_of_DRAM() and memblock_start_of_DRAM(), but I can't see that the order of initrd added to the memblock will affect
those two values returned from memblock_ fucntions, IMHO the initrd will be loaded to somewhere within the DRAM by firmware, is that correct?

Thanks,
Dennis  
>
> 
> > Signed-off-by: Dennis Chen <[email-masked]>
> > Cc: Mark Rutland <[email-masked]>
> > Cc: Steve Capper <[email-masked]>
> > Cc: Catalin Marinas <[email-masked]>
> > Cc: Ard Biesheuvel <[email-masked]>
> > Cc: Will Deacon <[email-masked]>
> > ---
> > arch/arm64/mm/init.c | 58 +++++++++++++++++++++++-----------------------------
> > 1 file changed, 26 insertions(+), 32 deletions(-)
> > 
> > diff --git a/arch/arm64/mm/init.c b/arch/arm64/mm/init.c
> > index 2ade7a6..cf26cdb 100644
> > --- a/arch/arm64/mm/init.c
> > +++ b/arch/arm64/mm/init.c
> > @@ -228,6 +228,29 @@ void __init arm64_memblock_init(void)
> >        memblock_add(__pa(_text), (u64)(_end - _text));
> >    }
> > 
> > +    if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {
> > +        extern u16 memstart_offset_seed;
> > +        u64 range = linear_region_size -
> > +                (memblock_end_of_DRAM() - memblock_start_of_DRAM());
> > +
> > +        /*
> > +         * If the size of the linear region exceeds, by a sufficient
> > +         * margin, the size of the region that the available physical
> > +         * memory spans, randomize the linear region as well.
> > +         */
> > +        if (memstart_offset_seed > 0 && range >= ARM64_MEMSTART_ALIGN) {
> > +            range = range / ARM64_MEMSTART_ALIGN + 1;
> > +            memstart_addr -= ARM64_MEMSTART_ALIGN *
> > +                     ((range * memstart_offset_seed) >> 16);
> > +        }
> > +    }
> > +
> > +    /*
> > +     * Register the kernel text, kernel data, initrd, and initial
> > +     * pagetables with memblock.
> > +     */
> > +    memblock_reserve(__pa(_text), _end - _text);
> > +
> >    if (IS_ENABLED(CONFIG_BLK_DEV_INITRD) && initrd_start) {
> >        /*
> >         * Add back the memory we just removed if it results in the
> > @@ -254,41 +277,12 @@ void __init arm64_memblock_init(void)
> >            memblock_remove(base, size); /* clear MEMBLOCK_ flags */
> >            memblock_add(base, size);
> >            memblock_reserve(base, size);
> > +            /* the generic initrd code expects virtual addresses */
> > +            initrd_start = __phys_to_virt(initrd_start);
> > +            initrd_end = __phys_to_virt(initrd_end);
> >        }
> >    }
> > 
> > -    if (IS_ENABLED(CONFIG_RANDOMIZE_BASE)) {
> > -        extern u16 memstart_offset_seed;
> > -        u64 range = linear_region_size -
> > -                (memblock_end_of_DRAM() - memblock_start_of_DRAM());
> > -
> > -        /*
> > -         * If the size of the linear region exceeds, by a sufficient
> > -         * margin, the size of the region that the available physical
> > -         * memory spans, randomize the linear region as well.
> > -         */
> > -        if (memstart_offset_seed > 0 && range >= ARM64_MEMSTART_ALIGN) {
> > -            range = range / ARM64_MEMSTART_ALIGN + 1;
> > -            memstart_addr -= ARM64_MEMSTART_ALIGN *
> > -                     ((range * memstart_offset_seed) >> 16);
> > -        }
> > -    }
> > -
> > -    /*
> > -     * Register the kernel text, kernel data, initrd, and initial
> > -     * pagetables with memblock.
> > -     */
> > -    memblock_reserve(__pa(_text), _end - _text);
> > -#ifdef CONFIG_BLK_DEV_INITRD
> > -    if (initrd_start) {
> > -        memblock_reserve(initrd_start, initrd_end - initrd_start);
> > -
> > -        /* the generic initrd code expects virtual addresses */
> > -        initrd_start = __phys_to_virt(initrd_start);
> > -        initrd_end = __phys_to_virt(initrd_end);
> > -    }
> > -#endif
> > -
> >    early_init_fdt_scan_reserved_mem();
> > 
> >    /* 4GB maximum for 32-bit only capable devices */
> > -- 
> > 1.8.3.1
> > 
>