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

From: Aditya Gupta <adityag@linux.ibm.com>
To: Baoquan He <bhe@redhat.com>
Cc: k-hagio-ab@nec.com, kexec@lists.infradead.org,
	Hari Bathini <hbathini@linux.ibm.com>,
	Mahesh J Salgaonkar <mahesh@linux.ibm.com>,
	Sourabh Jain <sourabhjain@linux.ibm.com>
Subject: Re: [PATCH] makedumpfile: ppc64: read cur_mmu_type from vmcoreinfo
Date: Fri, 23 Feb 2024 14:07:21 +0530	[thread overview]
Message-ID: <dzjnckicvqtflbtwh3omaccwcq5zw3i7ebyumtmnyd3quffwij@ircw5am7wrjr> (raw)
In-Reply-To: <ZdhPJKGd7wqbesVp@MiWiFi-R3L-srv>

On Fri, Feb 23, 2024 at 03:54:12PM +0800, Baoquan He wrote:
> Add maintainer Kazu to CC.

Thanks, I missed him, will resend this patch with him in CC.

Thanks,
Aditya Gupta

> 
> 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
> > 
> > 
> > _______________________________________________
> > kexec mailing list
> > kexec@lists.infradead.org
> > http://lists.infradead.org/mailman/listinfo/kexec
> > 
> 

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