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

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Message-ID: <f13e218e-4e38-4076-672f-d555d7abfc02@linux.ibm.com>
Date:   Mon, 4 Oct 2021 21:36:38 +0530
From:   "Aneesh Kumar K.V" <aneesh.kumar@...ux.ibm.com>
To:     Sourabh Jain <sourabhjain@...ux.ibm.com>, mpe@...erman.id.au
Cc:     hbathini@...ux.ibm.com, mahesh@...ux.vnet.ibm.com,
        linux-kernel@...r.kernel.org, linuxppc-dev@...abs.org,
        Abdul haleem <abdhalee@...ux.vnet.ibm.com>
Subject: Re: [PATCH 3/3] powerpc: Set crashkernel offset to mid of RMA region

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@...ux.ibm.com>
> Reported-and-tested-by: Abdul haleem <abdhalee@...ux.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
>