[PATCH] makedumpfile: ppc64: read cur_mmu_type from vmcoreinfo

[Aditya Gupta]

Hi Kazu,

On Wed, Feb 28, 2024 at 12:25:04AM +0000, HAGIO KAZUHITO(萩尾 一仁) wrote:
> On 2024/02/23 17:39, 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 at linux.ibm.com>
> 
> Thanks, applied.
> https://github.com/makedumpfile/makedumpfile/commit/71ac00c8a3464608ac19f7c89d7220073d7374a9

Thank you.

- Aditya Gupta

> 
> Kazu
> 
> > ---
> >   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 {