[PATCH] ARM: kexec: fix crashkernel= handling

[Russell King - ARM Linux]

On Wed, Mar 30, 2016 at 06:09:22PM +0530, Pratyush Anand wrote:
> On 30/03/2016:09:46:38 AM, Dave Young wrote:
> > Hi, Russell
> > 
> > A long standing issue, but nobody tried to do it. Thank you for bringing up.
> > 
> > On 03/29/16 at 11:10am, Russell King wrote:
> > > When the kernel crashkernel parameter is specified with just a size, we
> > > are supposed to allocate a region from RAM to store the crashkernel.
> > > However, ARM merely reserves physical address zero with no checking
> > > that there is even RAM there.
> > > 
> > > Fix this by lifting similar code from x86, importing it to ARM with
> > > the ARM specific parameters added.
> > > 
> > > Update the kdump documentation to reflect this change.
> > > 
> > > Signed-off-by: Russell King <rmk+kernel at arm.linux.org.uk>
> > > ---
> > >  Documentation/kdump/kdump.txt | 13 +++----------
> > >  arch/arm/kernel/setup.c       | 26 ++++++++++++++++++++++++++
> > >  2 files changed, 29 insertions(+), 10 deletions(-)
> > > 
> > > diff --git a/Documentation/kdump/kdump.txt b/Documentation/kdump/kdump.txt
> > > index bc4bd5a44b88..88ff63d5fde3 100644
> > > --- a/Documentation/kdump/kdump.txt
> > > +++ b/Documentation/kdump/kdump.txt
> > > @@ -263,12 +263,6 @@ been removed from the machine.
> > >      crashkernel=<range1>:<size1>[,<range2>:<size2>,...][@offset]
> > >      range=start-[end]
> > >  
> > > -Please note, on arm, the offset is required.
> > > -    crashkernel=<range1>:<size1>[,<range2>:<size2>,...]@offset
> > > -    range=start-[end]
> > > -
> > > -    'start' is inclusive and 'end' is exclusive.
> > > -
> > >  For example:
> > >  
> > >      crashkernel=512M-2G:64M,2G-:128M
> > > @@ -307,10 +301,9 @@ Boot into System Kernel
> > >     on the memory consumption of the kdump system. In general this is not
> > >     dependent on the memory size of the production system.
> > >  
> > > -   On arm, use "crashkernel=Y at X". Note that the start address of the kernel
> > > -   will be aligned to 128MiB (0x08000000), so if the start address is not then
> > > -   any space below the alignment point may be overwritten by the dump-capture kernel,
> > > -   which means it is possible that the vmcore is not that precise as expected.
> > > +   On arm, the use of "crashkernel=Y at X" is no longer necessary; the
> > > +   kernel will automatically locate the crash kernel image within the
> > > +   first 512MB of RAM if X is not given.
> > >  
> > >  
> > >  Load the Dump-capture Kernel
> > > diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
> > > index 7d0cba6f1cc5..5d8511c425f0 100644
> > > --- a/arch/arm/kernel/setup.c
> > > +++ b/arch/arm/kernel/setup.c
> > > @@ -938,6 +938,13 @@ static int __init init_machine_late(void)
> > >  late_initcall(init_machine_late);
> > >  
> > >  #ifdef CONFIG_KEXEC
> > > +/*
> > > + * The crash region must be aligned to 128MB to avoid
> > > + * zImage relocating below the reserved region.
> > > + */
> > > +#define CRASH_ALIGN	(128 << 20)
> > > +#define CRASH_ADDR_MAX	(PHYS_OFFSET + (512 << 20))
> > 
> > Any reason to limit crash mem within the first 512M only? What if one want to
> > reserve memory over 512M?
> 
> When crash base is not give, then may be it can be just checked if memblock
> region is memory and not reserved, then allow to reserve. That might help to
> remove 512M restriction.

... and then I'll have to update the commit text.

You may notice that I say that this is mostly taken from the x86
implementation.  The x86 implementation also has this 512MB
allocation limit, to prevent it being placed too high in physical
memory.

This limit only applies for the case where the user hasn't specified
the base.

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