[3/3] powerpc: Set crashkernel offset to mid of RMA region

On large config LPARs (having 192 and more cores), Linux fails to boot
due to insufficient memory in the first memory block. It is due to the
reserve crashkernel area starts at 128MB offset by default and which
doesn't leave enough space in the first memory block to accommodate
memory for other essential system resources.

Given that the RMA region size can be 512MB or more, setting the
crashkernel offset to mid of RMA size will leave enough space to
kernel to allocate memory for other system resources in the first
memory block.

Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com>
Reported-and-tested-by: Abdul haleem <abdhalee@linux.vnet.ibm.com>
---
 arch/powerpc/kernel/rtas.c |  3 +++
 arch/powerpc/kexec/core.c  | 13 +++++++++----
 2 files changed, 12 insertions(+), 4 deletions(-)

On 10/4/21 20:41, Sourabh Jain wrote:
> On large config LPARs (having 192 and more cores), Linux fails to boot
> due to insufficient memory in the first memory block. It is due to the
> reserve crashkernel area starts at 128MB offset by default and which
> doesn't leave enough space in the first memory block to accommodate
> memory for other essential system resources.
> 
> Given that the RMA region size can be 512MB or more, setting the
> crashkernel offset to mid of RMA size will leave enough space to
> kernel to allocate memory for other system resources in the first
> memory block.
> 
> Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com>
> Reported-and-tested-by: Abdul haleem <abdhalee@linux.vnet.ibm.com>
> ---
>   arch/powerpc/kernel/rtas.c |  3 +++
>   arch/powerpc/kexec/core.c  | 13 +++++++++----
>   2 files changed, 12 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c
> index ff80bbad22a5..ce5e62bb4d8e 100644
> --- a/arch/powerpc/kernel/rtas.c
> +++ b/arch/powerpc/kernel/rtas.c
> @@ -1235,6 +1235,9 @@ int __init early_init_dt_scan_rtas(unsigned long node,
>   	entryp = of_get_flat_dt_prop(node, "linux,rtas-entry", NULL);
>   	sizep  = of_get_flat_dt_prop(node, "rtas-size", NULL);
>   
> +	if (of_get_flat_dt_prop(node, "ibm,hypertas-functions", NULL))
> +		powerpc_firmware_features |= FW_FEATURE_LPAR;
> +

The equivalent check that we currently do more than checking 
ibm,hypertas-functions.

	if (!strcmp(uname, "rtas") || !strcmp(uname, "rtas@0")) {
		prop = of_get_flat_dt_prop(node, "ibm,hypertas-functions",
					   &len);
		if (prop) {
			powerpc_firmware_features |= FW_FEATURE_LPAR;
			fw_hypertas_feature_init(prop, len);
		}


also do we expect other firmware features to be set along with 
FW_FEATURE_LPAR?

>   	if (basep && entryp && sizep) {
>   		rtas.base = *basep;
>   		rtas.entry = *entryp;
> diff --git a/arch/powerpc/kexec/core.c b/arch/powerpc/kexec/core.c
> index 48525e8b5730..f69cf3e370ec 100644
> --- a/arch/powerpc/kexec/core.c
> +++ b/arch/powerpc/kexec/core.c
> @@ -147,11 +147,16 @@ void __init reserve_crashkernel(void)
>   	if (!crashk_res.start) {
>   #ifdef CONFIG_PPC64
>   		/*
> -		 * On 64bit we split the RMO in half but cap it at half of
> -		 * a small SLB (128MB) since the crash kernel needs to place
> -		 * itself and some stacks to be in the first segment.
> +		 * crash kernel needs to placed in the first segment. On LPAR
> +		 * setting crash kernel start to mid of RMA size (512MB or more)
> +		 * would help primary kernel to boot properly on large config
> +		 * LPAR (with core count 192 or more) and for the reset keep
> +		 * cap the crash kernel start at 128MB offse.
>   		 */
> -		crashk_res.start = min(0x8000000ULL, (ppc64_rma_size / 2));
> +		if (firmware_has_feature(FW_FEATURE_LPAR))
> +			crashk_res.start = ppc64_rma_size / 2;
> +		else
> +			crashk_res.start = min(0x8000000ULL, (ppc64_rma_size / 2));
>   #else
>   		crashk_res.start = KDUMP_KERNELBASE;
>   #endif
>

Hello Aneesh,

@@ -1235,6 +1235,9 @@ int __init early_init_dt_scan_rtas(unsigned long 
node,
>>       entryp = of_get_flat_dt_prop(node, "linux,rtas-entry", NULL);
>>       sizep  = of_get_flat_dt_prop(node, "rtas-size", NULL);
>>   +    if (of_get_flat_dt_prop(node, "ibm,hypertas-functions", NULL))
>> +        powerpc_firmware_features |= FW_FEATURE_LPAR;
>> +
>
> The equivalent check that we currently do more than checking 
> ibm,hypertas-functions.
>
>     if (!strcmp(uname, "rtas") || !strcmp(uname, "rtas@0")) {
>         prop = of_get_flat_dt_prop(node, "ibm,hypertas-functions",
>                        &len);
>         if (prop) {
>             powerpc_firmware_features |= FW_FEATURE_LPAR;
>             fw_hypertas_feature_init(prop, len);
> }
>
If ibm,hypertas-functions prop has to be part of rtas or rtas@0 node to 
decide we are on LPAR then how about splitting the probe_fw_features 
functions into two functions, one to detect FW_FEATURE_LPAR and another 
function to do the rest?
>
> also do we expect other firmware features to be set along with 
> FW_FEATURE_LPAR?


No only FW_FEATURE_LPAR feature so that kernel can decide the 
crashkernel offset accordingly.


Thanks for the review.

- Sourabh Jain

On 04/10/21 21:36, Aneesh Kumar K.V wrote:
> On 10/4/21 20:41, Sourabh Jain wrote:
>> On large config LPARs (having 192 and more cores), Linux fails to boot
>> due to insufficient memory in the first memory block. It is due to the
>> reserve crashkernel area starts at 128MB offset by default and which
>> doesn't leave enough space in the first memory block to accommodate
>> memory for other essential system resources.
>>
>> Given that the RMA region size can be 512MB or more, setting the
>> crashkernel offset to mid of RMA size will leave enough space to
>> kernel to allocate memory for other system resources in the first
>> memory block.
>>
>> Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com>
>> Reported-and-tested-by: Abdul haleem <abdhalee@linux.vnet.ibm.com>
>> ---
>>   arch/powerpc/kernel/rtas.c |  3 +++
>>   arch/powerpc/kexec/core.c  | 13 +++++++++----
>>   2 files changed, 12 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c
>> index ff80bbad22a5..ce5e62bb4d8e 100644
>> --- a/arch/powerpc/kernel/rtas.c
>> +++ b/arch/powerpc/kernel/rtas.c
>> @@ -1235,6 +1235,9 @@ int __init early_init_dt_scan_rtas(unsigned 
>> long node,
>>       entryp = of_get_flat_dt_prop(node, "linux,rtas-entry", NULL);
>>       sizep  = of_get_flat_dt_prop(node, "rtas-size", NULL);
>>   +    if (of_get_flat_dt_prop(node, "ibm,hypertas-functions", NULL))
>> +        powerpc_firmware_features |= FW_FEATURE_LPAR;
>> +
>
> The equivalent check that we currently do more than checking 
> ibm,hypertas-functions.
>
>     if (!strcmp(uname, "rtas") || !strcmp(uname, "rtas@0")) {
>         prop = of_get_flat_dt_prop(node, "ibm,hypertas-functions",
>                        &len);
>         if (prop) {
>             powerpc_firmware_features |= FW_FEATURE_LPAR;
>             fw_hypertas_feature_init(prop, len);
>         }
>
>
> also do we expect other firmware features to be set along with 
> FW_FEATURE_LPAR?

This patch needs to move crash kernel reservation to mid point of rma 
size for LPAR in reserve_crashkernel() function. Since 
reserve_crashkernel() is called too early even before 
powerpc_firmware_features is set with FW_FEATURE_LPAR, the check for if 
(firmware_has_feature(FW_FEATURE_LPAR)) fails and hence we only need to 
make sure that we set this flag early during early_init_dt_scan_rtas().

The rest of the LPAR specific initialization isn't required at this 
point and will be still done during pseries_probe_fw_features() as usual.

Thanks,
Sourabh Jain