Subject: [PATCH] ARM: kexec: fix crashkernel= handling

From: [email-masked] (Vivek Goyal)
Date: Wed, 30 Mar 2016 09:27:08 -0400

On Wed, Mar 30, 2016 at 02:05:30PM +0100, Russell King - ARM Linux wrote:
> 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 <[email-masked]>
> > > > ---
> > > >  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.

IIRC, x86 had this limitation as they could not support any higher. But
if ARM can support higher, it would be good to allow that.

Thanks
Vivek