Re: [PATCH v2] ppc64/kdump: Limit kdump base to 512MB

[Sachin Sant <sachinp@linux.ibm.com>]

> On 12-Sep-2022, at 12:20 PM, Hari Bathini <hbathini@linux.ibm.com> wrote:
> 
> 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. This change
> meant the offset is either 256MB or 512MB on LPARs as ppc64_rma_size
> was 512MB or 1024MB owing to commit 103a8542cb35b ("powerpc/book3s64/
> radix: Fix boot failure with large amount of guest memory")
> 
> But ppc64_rma_size can be larger as well with newer f/w. So, limit
> crashkernel reservation offset to 512MB to avoid running into boot
> failures during kdump kernel boot, due to RTAS or other allocation
> restrictions.
> 
> Also, while here, use SZ_128M instead of opening coding it.
> 
> Signed-off-by: Hari Bathini <hbathini@linux.ibm.com>
> ---

Tested on a Power10 and Power9 LPAR. Kdump works as expected.

Tested-by: Sachin Sant <sachinp@linux.ibm.com>

> 
> Changes in V2:
> * Updated the changelog for clarity.
> * Used SZ_512M instead of open coding as suggested by Christophe.
> * Used SZ_128M instead of open coding 128MB.
> 
> arch/powerpc/kexec/core.c | 6 +++---
> 1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/powerpc/kexec/core.c b/arch/powerpc/kexec/core.c
> index cf84bfe9e27e..de64c7962991 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
> @@ -144,9 +144,9 @@ 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_t(u64, ppc64_rma_size / 2, SZ_512M);
> 		else
> -			crashk_res.start = min(0x8000000ULL, (ppc64_rma_size / 2));
> +			crashk_res.start = min_t(u64, ppc64_rma_size / 2, SZ_128M);
> #else
> 		crashk_res.start = KDUMP_KERNELBASE;
> #endif
> -- 
> 2.37.3
>