[PATCH] ppc64/kdump: Limit kdump base to 512MB

[Hari Bathini]

On 12/09/22 10:54 am, Christophe Leroy wrote:
> 
> 
> Le 09/09/2022 à 19:40, Hari Bathini a écrit :
>> Since commit e641eb03ab2b0 ("powerpc: Fix up the kdump base cap to
>> 128M") memory for kdump kernel has been reserved at an offset of
>> 128MB. This held up well for a long time before running into boot
>> failure on LPARs having a lot of cores. Commit 7c5ed82b800d8
>> ("powerpc: Set crashkernel offset to mid of RMA region") fixed this
>> boot failure by moving the offset to mid of RMA region. Limit this
>> offset to 512MB to avoid running into boot failures, during kdump
>> kernel boot, due RTAS or other allocation restrictions.
>>
>> Signed-off-by: Hari Bathini <hbathini at linux.ibm.com>
>> ---
>>    arch/powerpc/kexec/core.c | 4 ++--
>>    1 file changed, 2 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/powerpc/kexec/core.c b/arch/powerpc/kexec/core.c
>> index cf84bfe9e27e..c2cbfcf81cea 100644
>> --- a/arch/powerpc/kexec/core.c
>> +++ b/arch/powerpc/kexec/core.c
>> @@ -136,7 +136,7 @@ void __init reserve_crashkernel(void)
>>    #ifdef CONFIG_PPC64
>>    		/*
>>    		 * On the LPAR platform place the crash kernel to mid of
>> -		 * RMA size (512MB or more) to ensure the crash kernel
>> +		 * RMA size (max. of 512MB) to ensure the crash kernel
>>    		 * gets enough space to place itself and some stack to be
>>    		 * in the first segment. At the same time normal kernel
>>    		 * also get enough space to allocate memory for essential
>> @@ -144,7 +144,7 @@ void __init reserve_crashkernel(void)
>>    		 * kernel starts at 128MB offset on other platforms.
>>    		 */
>>    		if (firmware_has_feature(FW_FEATURE_LPAR))
>> -			crashk_res.start = ppc64_rma_size / 2;
>> +			crashk_res.start = min(0x20000000ULL, (ppc64_rma_size / 2));
> 
> Use SZ_512M instead of open coding.
> 
> Remove the ( ) around ppc64_rma_size / 2

Thanks for the review. Posted v2 with updated changelog and
the above addressed..

- Hari