Re: [PATCH] makedumpfile: ppc64: read cur_mmu_type from vmcoreinfo

[Baoquan He <bhe@redhat.com>]

Add maintainer Kazu to CC.

On 02/23/24 at 11:23am, Aditya Gupta wrote:
> Currently makedumpfile depends on reading the 'cur_cpu_spec' kernel
> symbol to get the current MMU type on PowerPC64.
> 
> The disadvantage with this approach was that it depends on bit '0x40'
> ('MMU_FTR_TYPE_RADIX') being set in 'cur_cpu_spec->mmu_features',
> which implies kernel developers have to be careful of modifying
> MMU_FTR_* defines
> 
> Instead a more stable approach was suggested by contributors in
> https://lore.kernel.org/linuxppc-dev/87v8c3m70t.fsf@mail.lhotse/, to
> pass information about the MMU type in vmcoreinfo itself, instead of
> depending on the MMU_FTR_* defines
> 
> This was implemented in linux kernel in:
>     commit 36e826b568e4 ("powerpc/vmcore: Add MMU information to vmcoreinfo")
> 
> With this commit, if RADIX_MMU is there in the vmcoreinfo, we prefer it
> to get current mmu type, instead of 'cur_cpu_spec'.
> On older kernels, where RADIX_MMU number is not there, makedumpfile will
> simply fall back to using 'cur_cpu_spec'.
> 
> The earlier defines for 'RADIX_MMU' have been renamed to 'MMU_TYPE_RADIX'
> which avoids conflict with the vmcoreinfo string 'RADIX_MMU', as well as
> being more clear about the value 0x40 with a comment about MMU_FTR_TYPE_RADIX
> 
> Signed-off-by: Aditya Gupta <adityag@linux.ibm.com>
> ---
>  arch/ppc64.c   | 15 ++++++++++-----
>  makedumpfile.c |  1 +
>  makedumpfile.h |  9 ++++++---
>  3 files changed, 17 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/ppc64.c b/arch/ppc64.c
> index 96c357cb0335..3b4f91981f71 100644
> --- a/arch/ppc64.c
> +++ b/arch/ppc64.c
> @@ -250,7 +250,7 @@ ppc64_vmalloc_init(void)
>  		/*
>  		 * 64K pagesize
>  		 */
> -		if (info->cur_mmu_type & RADIX_MMU) {
> +		if (info->cur_mmu_type & MMU_TYPE_RADIX) {
>  			info->l1_index_size = PTE_INDEX_SIZE_RADIX_64K;
>  			info->l2_index_size = PMD_INDEX_SIZE_RADIX_64K;
>  			info->l3_index_size = PUD_INDEX_SIZE_RADIX_64K;
> @@ -300,7 +300,7 @@ ppc64_vmalloc_init(void)
>  		/*
>  		 * 4K pagesize
>  		 */
> -		if (info->cur_mmu_type & RADIX_MMU) {
> +		if (info->cur_mmu_type & MMU_TYPE_RADIX) {
>  			info->l1_index_size = PTE_INDEX_SIZE_RADIX_4K;
>  			info->l2_index_size = PMD_INDEX_SIZE_RADIX_4K;
>  			info->l3_index_size = PUD_INDEX_SIZE_RADIX_4K;
> @@ -635,14 +635,19 @@ get_versiondep_info_ppc64()
>  	 * On PowerISA 3.0 based server processors, a kernel can run with
>  	 * radix MMU or standard MMU. Get the current MMU type.
>  	 */
> -	info->cur_mmu_type = STD_MMU;
> -	if ((SYMBOL(cur_cpu_spec) != NOT_FOUND_SYMBOL)
> +	info->cur_mmu_type = MMU_TYPE_STD;
> +
> +	if (NUMBER(RADIX_MMU) != NOT_FOUND_SYMBOL) {
> +		if (NUMBER(RADIX_MMU) == 1) {
> +			info->cur_mmu_type = MMU_TYPE_RADIX;
> +		}
> +	} else if ((SYMBOL(cur_cpu_spec) != NOT_FOUND_SYMBOL)
>  	    && (OFFSET(cpu_spec.mmu_features) != NOT_FOUND_STRUCTURE)) {
>  		if (readmem(VADDR, SYMBOL(cur_cpu_spec), &cur_cpu_spec,
>  		    sizeof(cur_cpu_spec))) {
>  			if (readmem(VADDR, cur_cpu_spec + OFFSET(cpu_spec.mmu_features),
>  			    &mmu_features, sizeof(mmu_features)))
> -				info->cur_mmu_type = mmu_features & RADIX_MMU;
> +				info->cur_mmu_type = mmu_features & MMU_TYPE_RADIX;
>  		}
>  	}
>  
> diff --git a/makedumpfile.c b/makedumpfile.c
> index 3705bdd93deb..1bd7305f49ca 100644
> --- a/makedumpfile.c
> +++ b/makedumpfile.c
> @@ -2987,6 +2987,7 @@ read_vmcoreinfo(void)
>  #endif
>  
>  	READ_NUMBER("HUGETLB_PAGE_DTOR", HUGETLB_PAGE_DTOR);
> +	READ_NUMBER("RADIX_MMU", RADIX_MMU);
>  
>  	return TRUE;
>  }
> diff --git a/makedumpfile.h b/makedumpfile.h
> index 3ed3ba551d96..a7b344974636 100644
> --- a/makedumpfile.h
> +++ b/makedumpfile.h
> @@ -747,12 +747,13 @@ unsigned long get_kvbase_arm64(void);
>  /*
>   * Supported MMU types
>   */
> -#define STD_MMU         0x0
> +#define MMU_TYPE_STD         0x0
>  /*
>   * The flag bit for radix MMU in cpu_spec.mmu_features
> - * in the kernel. Use the same flag here.
> + * in the kernel (MMU_FTR_TYPE_RADIX).
> + * Use the same flag here.
>   */
> -#define RADIX_MMU       0x40
> +#define MMU_TYPE_RADIX       0x40
>  
>  
>  #define PGD_MASK_L4		\
> @@ -2258,6 +2259,8 @@ struct number_table {
>  	unsigned long kernel_link_addr;
>  	unsigned long va_kernel_pa_offset;
>  #endif
> +
> +	unsigned long RADIX_MMU;
>  };
>  
>  struct srcfile_table {
> -- 
> 2.43.0
> 
> 
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