[PATCH 03/12] ARM: kexec: remove 512MB restriction on kexec crashdump

[Pratyush Anand]

On Fri, Apr 29, 2016 at 11:40 PM, Russell King - ARM Linux
<linux at arm.linux.org.uk> wrote:
> On Fri, Apr 29, 2016 at 07:49:45PM +0530, Pratyush Anand wrote:
>> On Thu, Apr 28, 2016 at 2:57 PM, Russell King
>> <rmk+kernel at arm.linux.org.uk> wrote:
>> > Signed-off-by: Russell King <rmk+kernel at arm.linux.org.uk>
>> > ---
>> >  arch/arm/kernel/setup.c | 5 +----
>> >  1 file changed, 1 insertion(+), 4 deletions(-)
>> >
>> > diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
>> > index 77b54c461c52..d9317eec1eba 100644
>> > --- a/arch/arm/kernel/setup.c
>> > +++ b/arch/arm/kernel/setup.c
>> > @@ -943,7 +943,6 @@ late_initcall(init_machine_late);
>> >   * zImage relocating below the reserved region.
>> >   */
>> >  #define CRASH_ALIGN    (128 << 20)
>> > -#define CRASH_ADDR_MAX (PHYS_OFFSET + (512 << 20))
>> >
>> >  static inline unsigned long long get_total_mem(void)
>> >  {
>> > @@ -973,9 +972,7 @@ static void __init reserve_crashkernel(void)
>> >                 return;
>> >
>> >         if (crash_base <= 0) {
>> > -               unsigned long long crash_max = CRASH_ADDR_MAX;
>> > -               if (crash_max > (u32)~0)
>> > -                       crash_max = (u32)~0;
>> > +               unsigned long long crash_max = idmap_to_phys((u32)~0);
>> >                 crash_base = memblock_find_in_range(CRASH_ALIGN, crash_max,
>> >                                                     crash_size, CRASH_ALIGN);
>> >                 if (!crash_base) {
>>
>> Reviewed-by: Pratyush Anand <panand at redhat.com>
>>
>> Unrelated to these modification:
>> In function arch/arm/mm/init.c: arm_memblock_steal() may be  following
>> would be more appropriate?
>> memblock_alloc_base(size, align, idmap_to_phys(MEMBLOCK_ALLOC_ANYWHERE));
>
> No, arm_memblock_steal() is totally unsuitable.  arm_memblock_steal()
> *removes* the memory range from memblock, including removing the
> mapping of that memory.  It will make the memory range inaccessible to
> the kernel.
>
> Since kexec wants to write directly to this memory, using
> arm_memblock_steal() will have the cause the kernel to OOPS when
> it hits the resulting hole.
>

Sorry, I was not trying to say that we should use arm_memblock_steal()
here. As I said, this comment is totally unrelated to this patch
series. In arm_memblock_steal() we pass MEMBLOCK_ALLOC_ANYWHERE as
max_addr. Probably,  it would be good to pass
idmap_to_phys(MEMBLOCK_ALLOC_ANYWHERE).