[PATCH 1/2] ARM: kexec: avoid allocating crashkernel region outside lowmem

[Keerthy]

On Thursday 20 July 2017 01:40 PM, Russell King wrote:
> Allocating the crashkernel region outside lowmem causes the kernel to
> oops while trying to kexec into the new kernel:
> 
> Loading crashdump kernel...
> Unable to handle kernel NULL pointer dereference at virtual address 00000000
> pgd = edd70000
> [00000000] *pgd=de19e835
> Internal error: Oops: 817 [#2] SMP ARM
> Modules linked in: ...
> CPU: 0 PID: 689 Comm: sh Not tainted 4.12.0-rc3-next-20170601-04015-gc3a5a20
> Hardware name: Generic DRA74X (Flattened Device Tree)
> task: edb32f00 task.stack: edf18000
> PC is at memcpy+0x50/0x330
> LR is at 0xe3c34001
> pc : [<c04baf30>]    lr : [<e3c34001>]    psr: 800c0193
> sp : edf19c2c  ip : 0a000001  fp : c0553170
> r10: c055316e  r9 : 00000001  r8 : e3130001
> r7 : e4903004  r6 : 0a000014  r5 : e3500000  r4 : e59f106c
> r3 : e59f0074  r2 : ffffffe8  r1 : c010fb88  r0 : 00000000
> Flags: Nzcv  IRQs off  FIQs on  Mode SVC_32  ISA ARM  Segment none
> Control: 10c5387d  Table: add7006a  DAC: 00000051
> Process sh (pid: 689, stack limit = 0xedf18218)
> Stack: (0xedf19c2c to 0xedf1a000)
> ...
> [<c04baf30>] (memcpy) from [<c010fae0>] (machine_kexec+0xa8/0x12c)
> [<c010fae0>] (machine_kexec) from [<c01e4104>] (__crash_kexec+0x5c/0x98)
> [<c01e4104>] (__crash_kexec) from [<c01e419c>] (crash_kexec+0x5c/0x68)
> [<c01e419c>] (crash_kexec) from [<c010c5c0>] (die+0x228/0x490)
> [<c010c5c0>] (die) from [<c011e520>] (__do_kernel_fault.part.0+0x54/0x1e4)
> [<c011e520>] (__do_kernel_fault.part.0) from [<c082412c>] (do_page_fault+0x1e8/0x400)
> [<c082412c>] (do_page_fault) from [<c010135c>] (do_DataAbort+0x38/0xb8)
> [<c010135c>] (do_DataAbort) from [<c0823584>] (__dabt_svc+0x64/0xa0)
> 
> This is caused by image->control_code_page being a highmem page, so
> page_address(image->control_code_page) returns NULL.  In any case, we
> don't want the control page to be a highmem page.
> 
> We already limit the crash kernel region to the top of 32-bit physical
> memory space.  Also limit it to the top of lowmem in physical space.
> 

Tested loading crash kernel on DRA7-EVM

Tested-by: Keerthy <j-keerthy at ti.com>

> Reported-by: Keerthy <j-keerthy at ti.com>
> Signed-off-by: Russell King <rmk+kernel at armlinux.org.uk>
> ---
>  arch/arm/kernel/setup.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
> index 4e80bf7420d4..8e9a3e40d949 100644
> --- a/arch/arm/kernel/setup.c
> +++ b/arch/arm/kernel/setup.c
> @@ -987,6 +987,9 @@ static void __init reserve_crashkernel(void)
>  
>  	if (crash_base <= 0) {
>  		unsigned long long crash_max = idmap_to_phys((u32)~0);
> +		unsigned long long lowmem_max = __pa(high_memory - 1) + 1;
> +		if (crash_max > lowmem_max)
> +			crash_max = lowmem_max;
>  		crash_base = memblock_find_in_range(CRASH_ALIGN, crash_max,
>  						    crash_size, CRASH_ALIGN);
>  		if (!crash_base) {
>