[PATCH 0/3] Update crashkernel offset to allow kernel to boot on large config LPARs

[PATCH 0/3] Update crashkernel offset to allow kernel to boot on large config LPARs

[Sourabh Jain]

As the crashkernel reserve memory at 128MB offset in the first memory
block, it leaves less than 128MB memory to accommodate other essential
system resources that need memory reservation in the same block. This
creates kernel boot failure on large config LPARs having core count
greater than 192.

Setting the crashkernel to mid of RMA size which can be 512MB or more
instead of capping it to 128MB by default leaves enough space to allocate
memory to another system resource in the first memory block.

Now keeping the crashkernel at mid of RMA size works fine for the primary
kernel but creates boot failure for the kdump kernel when the crashekernel
reservation start offset crosses 256MB. The reason is, in the early boot
MMU feature of 1T segments support is not detected which restricts the paca
allocation for boot CPU below 256MB. When the crashkernel itself is
starting at 256MB offset, attempt to allocate paca below 256MB leads to the
kdump kernel boot failure.

Moving the detection of segment sizes before identifying the boot CPU
removes the restriction of 256MB limit for boot CPU paca allocation
which allows the kdump kernel to successfully boot and capture vmcore.

While allocating paca for boot CPU we found that there is a small window
during kernel boot where early_radix_enabled returns True even though
the radix is disabled using command-line. This leads to an invalid bolated
size calculation on which paca limit of boot CPU is dependent. Patch 0001
closes that window that by fixing the radix bit in mmu_feature.

changes in v2:
	0001: Rename the function name to update_cpu_features() as per
	      the review comment.
	0002: Fixed compilation error reported by kernel test robot.
	0003: Added comment and updated commit message

Mahesh Salgaonkar (2):
  fixup mmu_features immediately after getting cpu pa features.
  Remove 256MB limit restriction for boot cpu paca allocation

Sourabh Jain (1):
  powerpc: Set crashkernel offset to mid of RMA region

 arch/powerpc/include/asm/book3s/64/mmu.h |  2 ++
 arch/powerpc/include/asm/mmu.h           |  1 +
 arch/powerpc/kernel/prom.c               |  8 ++++++++
 arch/powerpc/kernel/rtas.c               |  4 ++++
 arch/powerpc/kexec/core.c                | 15 +++++++++++----
 arch/powerpc/mm/book3s64/hash_utils.c    |  5 ++++-
 arch/powerpc/mm/init_64.c                |  5 ++++-
 7 files changed, 34 insertions(+), 6 deletions(-)

-- 
2.31.1

[PATCH 1/3] fixup mmu_features immediately after getting cpu pa features.

[Sourabh Jain]

From: Mahesh Salgaonkar <mahesh@linux.ibm.com>

On system with radix support available, early_radix_enabled() starts
returning true for a small window (until mmu_early_init_devtree() is
called) even when radix mode disabled on kernel command line. This causes
ppc64_bolted_size() to return ULONG_MAX in HPT mode instead of supported
segment size, during boot cpu paca allocation.

Withi kernel command line = "... disable_radix":

early_init_devtree:			  <- early_radix_enabled() = false
  early_init_dt_scan_cpus:		  <- early_radix_enabled() = false
      ...
      check_cpu_pa_features:		  <- early_radix_enabled() = false
      ...				^ <- early_radix_enabled() = TRUE
      allocate_paca:			| <- early_radix_enabled() = TRUE
          ...                           |
          ppc64_bolted_size:		| <- early_radix_enabled() = TRUE
              if (early_radix_enabled())| <- early_radix_enabled() = TRUE
                  return ULONG_MAX;     |
      ...                               |
  ...					| <- early_radix_enabled() = TRUE
  ...					| <- early_radix_enabled() = TRUE
  mmu_early_init_devtree()              V
  ...					  <- early_radix_enabled() = false

So far we have not seen any issue because allocate_paca() takes minimum of
ppc64_bolted_size and rma_size while allocating paca. However it is better
to close this window by fixing up the mmu features as early as possible.
This fixes early_radix_enabled() and ppc64_bolted_size() to return valid
values in radix disable mode. This patch will help subsequent patch to
depend on early_radix_enabled() check while detecting supported segment
size in HPT mode.

Signed-off-by: Mahesh Salgaonkar <mahesh@linux.ibm.com>
Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com>
Reported-and-tested-by: Abdul haleem <abdhalee@linux.vnet.ibm.com>
---
 arch/powerpc/include/asm/book3s/64/mmu.h | 1 +
 arch/powerpc/include/asm/mmu.h           | 1 +
 arch/powerpc/kernel/prom.c               | 2 ++
 arch/powerpc/mm/init_64.c                | 5 ++++-
 4 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/include/asm/book3s/64/mmu.h b/arch/powerpc/include/asm/book3s/64/mmu.h
index c02f42d1031e..d60be5051d60 100644
--- a/arch/powerpc/include/asm/book3s/64/mmu.h
+++ b/arch/powerpc/include/asm/book3s/64/mmu.h
@@ -197,6 +197,7 @@ extern int mmu_vmemmap_psize;
 extern int mmu_io_psize;
 
 /* MMU initialization */
+void update_cpu_features(void);
 void mmu_early_init_devtree(void);
 void hash__early_init_devtree(void);
 void radix__early_init_devtree(void);
diff --git a/arch/powerpc/include/asm/mmu.h b/arch/powerpc/include/asm/mmu.h
index 8abe8e42e045..5eb494ea85d7 100644
--- a/arch/powerpc/include/asm/mmu.h
+++ b/arch/powerpc/include/asm/mmu.h
@@ -401,6 +401,7 @@ extern void early_init_mmu(void);
 extern void early_init_mmu_secondary(void);
 extern void setup_initial_memory_limit(phys_addr_t first_memblock_base,
 				       phys_addr_t first_memblock_size);
+static inline void update_cpu_features(void) { }
 static inline void mmu_early_init_devtree(void) { }
 
 static inline void pkey_early_init_devtree(void) {}
diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
index 2e67588f6f6e..889c909e4ed4 100644
--- a/arch/powerpc/kernel/prom.c
+++ b/arch/powerpc/kernel/prom.c
@@ -380,6 +380,8 @@ static int __init early_init_dt_scan_cpus(unsigned long node,
 		check_cpu_pa_features(node);
 	}
 
+	/* Update cpu features based on kernel command line */
+	update_cpu_features();
 	identical_pvr_fixup(node);
 	init_mmu_slb_size(node);
 
diff --git a/arch/powerpc/mm/init_64.c b/arch/powerpc/mm/init_64.c
index 386be136026e..19680b42898f 100644
--- a/arch/powerpc/mm/init_64.c
+++ b/arch/powerpc/mm/init_64.c
@@ -437,12 +437,15 @@ static void __init early_check_vec5(void)
 	}
 }
 
-void __init mmu_early_init_devtree(void)
+void __init update_cpu_features(void)
 {
 	/* Disable radix mode based on kernel command line. */
 	if (disable_radix)
 		cur_cpu_spec->mmu_features &= ~MMU_FTR_TYPE_RADIX;
+}
 
+void __init mmu_early_init_devtree(void)
+{
 	/*
 	 * Check /chosen/ibm,architecture-vec-5 if running as a guest.
 	 * When running bare-metal, we can use radix if we like
-- 
2.31.1

[PATCH 2/3] Remove 256MB limit restriction for boot cpu paca allocation

[Sourabh Jain]

From: Mahesh Salgaonkar <mahesh@linux.ibm.com>

At the time when we detect and allocate paca for boot cpu, we havn't yet
detected mmu feature of 1T segments support (not until
mmu_early_init_devtree() call). This causes ppc64_bolted_size() to return
256MB as limit forcing boot cpu paca allocation below 256MB always.

This works fine for kdump kernel boot as long as crashkernel reservation is
at offset below 256MB. But when we move kdump offset to 256MB or above,
kdump kernel fails to allocate paca for boot cpu below 256MB and crashes in
allocate_paca().

Moving the detection of segment sizes just before paca allocation for boot
cpu removes this restriction of 256MB limit. This allows kdump kernel to
successfully boot and capture vmcore.

Signed-off-by: Mahesh Salgaonkar <mahesh@linux.ibm.com>
Signed-off-by: Sourabh Jain <sourabhjain@linux.ibm.com>
Reported-and-tested-by: Abdul haleem <abdhalee@linux.vnet.ibm.com>
---
 arch/powerpc/include/asm/book3s/64/mmu.h | 1 +
 arch/powerpc/kernel/prom.c               | 6 ++++++
 arch/powerpc/mm/book3s64/hash_utils.c    | 5 ++++-
 3 files changed, 11 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/include/asm/book3s/64/mmu.h b/arch/powerpc/include/asm/book3s/64/mmu.h
index d60be5051d60..9b05a84313bb 100644
--- a/arch/powerpc/include/asm/book3s/64/mmu.h
+++ b/arch/powerpc/include/asm/book3s/64/mmu.h
@@ -199,6 +199,7 @@ extern int mmu_io_psize;
 /* MMU initialization */
 void update_cpu_features(void);
 void mmu_early_init_devtree(void);
+void hash__early_detect_seg_size(void);
 void hash__early_init_devtree(void);
 void radix__early_init_devtree(void);
 #ifdef CONFIG_PPC_PKEY
diff --git a/arch/powerpc/kernel/prom.c b/arch/powerpc/kernel/prom.c
index 889c909e4ed4..5da2bfff4dea 100644
--- a/arch/powerpc/kernel/prom.c
+++ b/arch/powerpc/kernel/prom.c
@@ -385,6 +385,12 @@ static int __init early_init_dt_scan_cpus(unsigned long node,
 	identical_pvr_fixup(node);
 	init_mmu_slb_size(node);
 
+#ifdef CONFIG_PPC_BOOK3S_64
+	/* Initialize segment sizes */
+	if (!early_radix_enabled())
+		hash__early_detect_seg_size();
+#endif
+
 #ifdef CONFIG_PPC64
 	if (nthreads == 1)
 		cur_cpu_spec->cpu_features &= ~CPU_FTR_SMT;
diff --git a/arch/powerpc/mm/book3s64/hash_utils.c b/arch/powerpc/mm/book3s64/hash_utils.c
index c145776d3ae5..ef4fc6bb1b30 100644
--- a/arch/powerpc/mm/book3s64/hash_utils.c
+++ b/arch/powerpc/mm/book3s64/hash_utils.c
@@ -1020,11 +1020,14 @@ static void __init htab_initialize(void)
 #undef KB
 #undef MB
 
-void __init hash__early_init_devtree(void)
+void __init hash__early_detect_seg_size(void)
 {
 	/* Initialize segment sizes */
 	of_scan_flat_dt(htab_dt_scan_seg_sizes, NULL);
+}
 
+void __init hash__early_init_devtree(void)
+{
 	/* Initialize page sizes */
 	htab_scan_page_sizes();
 }
-- 
2.31.1

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

[Sourabh Jain]

On large config LPARs (having 192 and more cores), Linux fails to boot
due to insufficient memory in the first memblock. It is due to the
memory reservation for the crash kernel which starts at 128MB offset of
the first memblock. This memory reservation for the crash kernel doesn't
leave enough space in the first memblock to accommodate other essential
system resources.

The crash kernel start address was set to 128MB offset by default to
ensure that the crash kernel get some memory below the RMA region which
is used to be of size 256MB. But given that the RMA region size can be
512MB or more, setting the crash kernel offset to mid of RMA size will
leave enough space for kernel to allocate memory for other system
resources.

Since the above crash kernel offset change is only applicable to the LPAR
platform, the LPAR feature detection is pushed before the crash kernel
reservation. The rest of LPAR specific initialization will still
be done during pseries_probe_fw_features as usual.

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 |  4 ++++
 arch/powerpc/kexec/core.c  | 15 +++++++++++----
 2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c
index ff80bbad22a5..a49137727370 100644
--- a/arch/powerpc/kernel/rtas.c
+++ b/arch/powerpc/kernel/rtas.c
@@ -1235,6 +1235,10 @@ 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);
 
+	/* need this feature to decide the crashkernel offset */
+	if (of_get_flat_dt_prop(node, "ibm,hypertas-functions", NULL))
+		powerpc_firmware_features |= 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..71b1bfdadd76 100644
--- a/arch/powerpc/kexec/core.c
+++ b/arch/powerpc/kexec/core.c
@@ -147,11 +147,18 @@ 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.
+		 * On the LPAR platform place the crash kernel to mid of
+		 * RMA size (512MB or more) 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
+		 * system resource in the first segment. Keep the crash
+		 * kernel starts at 128MB offset on other platforms.
 		 */
-		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
-- 
2.31.1

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

[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

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

[Sourabh Jain]

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

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

[Aneesh Kumar K.V]

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
> 

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

[Sourabh Jain]

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;
+
 	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
-- 
2.31.1