Subject: Re: [PATCH v2] powerpc/mm: export current mmu mode info

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Thu, 22 Sep 2016 21:54:56 +0530

Hari Bathini <[email-masked]> writes:

> The kernel now supports both radix and hash MMU modes. Tools like crash
> and makedumpfile need to know the current MMU mode the kernel is using,
> to debug/analyze it.  The current MMU mode depends on hardware support
> and also whether disable_radix cmdline parameter is passed to the kernel.
> The mmu_features member of cpu_spec structure holds the current MMU mode
> a cpu is using. But the above mentioned tools need to know the MMU mode
> early in their init process, when they may not have access to offset info
> of structure members. A hard-coded offset may help but it won't be robust.

IIUC, you walk the linux page table and that should be more or less same
between radix/hash right except few bits. Now what crash will be
interested in will be the RPN part of the table which should be same
between hash/radix.

>
> This patch introduces a new global variable, which holds the current MMU
> mode the kernel is running in and can be accessed by tools early in thier
> init process,

Init process of what ? kernel or crash tool ?

>helping tools to initialize accurately for each MMU mode.
> This patch also optimizes the radix_enabled() function call.
>

how do you differentiate between the hold linux page table format and
the new ? Can you also summarize what crash tool look for in the page
table ?

> Signed-off-by: Hari Bathini <[email-masked]>
> ---
>
> Changes from v1:
> * Patch name changed from "ppc64/book3s: export mmu type info"
> * Optimized radix_enabled() function
>
>
>  arch/powerpc/include/asm/mmu.h      |   22 +++++++++++++++++++++-
>  arch/powerpc/kernel/machine_kexec.c |    3 +++
>  arch/powerpc/mm/hash_utils_64.c     |    2 ++
>  arch/powerpc/mm/pgtable-radix.c     |    2 ++
>  arch/powerpc/mm/pgtable.c           |    6 ++++++
>  arch/powerpc/mm/tlb_hash32.c        |    1 +
>  arch/powerpc/mm/tlb_nohash.c        |    2 ++
>  7 files changed, 37 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/include/asm/mmu.h b/arch/powerpc/include/asm/mmu.h
> index e2fb408..558987c 100644
> --- a/arch/powerpc/include/asm/mmu.h
> +++ b/arch/powerpc/include/asm/mmu.h
> @@ -199,6 +199,21 @@ static inline void mmu_clear_feature(unsigned long feature)
>
>  extern unsigned int __start___mmu_ftr_fixup, __stop___mmu_ftr_fixup;
>
> +/*
> + * Possible MMU modes
> + */
> +#define MMU_MODE_NONE           0
> +#define MMU_MODE_RADIX          1
> +#define MMU_MODE_HASH           2
> +#define MMU_MODE_HASH32         3
> +#define MMU_MODE_NOHASH         4
> +#define MMU_MODE_NOHASH32       5
> +
> +/*
> + * current MMU mode
> + */
> +extern unsigned int current_mmu_mode __read_mostly;
> +
>  #ifdef CONFIG_PPC64
>  /* This is our real memory area size on ppc64 server, on embedded, we
>   * make it match the size our of bolted TLB area
> @@ -218,7 +233,12 @@ static inline void assert_pte_locked(struct mm_struct *mm, unsigned long addr)
>  #ifdef CONFIG_PPC_RADIX_MMU
>  static inline bool radix_enabled(void)
>  {
> -	return mmu_has_feature(MMU_FTR_TYPE_RADIX);
> +	if (current_mmu_mode == MMU_MODE_RADIX)
> +		return true;
> +	else if (current_mmu_mode != MMU_MODE_NONE)
> +		return false;
> +	else
> +		return mmu_has_feature(MMU_FTR_TYPE_RADIX);
>  }
>

That is not optimization, that makes it slow. We hotpatch mmu_has_feature().

>  static inline bool early_radix_enabled(void)
> diff --git a/arch/powerpc/kernel/machine_kexec.c b/arch/powerpc/kernel/machine_kexec.c
> index 2694d07..4ecc184 100644
> --- a/arch/powerpc/kernel/machine_kexec.c
> +++ b/arch/powerpc/kernel/machine_kexec.c
> @@ -77,6 +77,9 @@ void arch_crash_save_vmcoreinfo(void)
>  	VMCOREINFO_SYMBOL(contig_page_data);
>  #endif
>  #if defined(CONFIG_PPC64) && defined(CONFIG_SPARSEMEM_VMEMMAP)
> +#ifdef CONFIG_PPC_BOOK3S
> +	VMCOREINFO_SYMBOL(current_mmu_mode);
> +#endif
>  	VMCOREINFO_SYMBOL(vmemmap_list);
>  	VMCOREINFO_SYMBOL(mmu_vmemmap_psize);
>  	VMCOREINFO_SYMBOL(mmu_psize_defs);
> diff --git a/arch/powerpc/mm/hash_utils_64.c b/arch/powerpc/mm/hash_utils_64.c
> index 0821556..a566a95 100644
> --- a/arch/powerpc/mm/hash_utils_64.c
> +++ b/arch/powerpc/mm/hash_utils_64.c
> @@ -886,6 +886,8 @@ void __init hash__early_init_devtree(void)
>
>  void __init hash__early_init_mmu(void)
>  {
> +	current_mmu_mode = MMU_MODE_HASH;
> +
>  	htab_init_page_sizes();
>
>  	/*
> diff --git a/arch/powerpc/mm/pgtable-radix.c b/arch/powerpc/mm/pgtable-radix.c
> index af897d9..4b0ad48 100644
> --- a/arch/powerpc/mm/pgtable-radix.c
> +++ b/arch/powerpc/mm/pgtable-radix.c
> @@ -298,6 +298,8 @@ void __init radix__early_init_mmu(void)
>  {
>  	unsigned long lpcr;
>
> +	current_mmu_mode = MMU_MODE_RADIX;
> +
>  #ifdef CONFIG_PPC_64K_PAGES
>  	/* PAGE_SIZE mappings */
>  	mmu_virtual_psize = MMU_PAGE_64K;
> diff --git a/arch/powerpc/mm/pgtable.c b/arch/powerpc/mm/pgtable.c
> index 0b6fb24..4638a00 100644
> --- a/arch/powerpc/mm/pgtable.c
> +++ b/arch/powerpc/mm/pgtable.c
> @@ -31,6 +31,12 @@
>  #include <asm/tlbflush.h>
>  #include <asm/tlb.h>
>
> +/*
> + * current MMU mode
> + */
> +unsigned int current_mmu_mode __read_mostly = MMU_MODE_NONE;
> +EXPORT_SYMBOL(current_mmu_mode);
> +
>  static inline int is_exec_fault(void)
>  {
>  	return current->thread.regs && TRAP(current->thread.regs) == 0x400;
> diff --git a/arch/powerpc/mm/tlb_hash32.c b/arch/powerpc/mm/tlb_hash32.c
> index 702d768..0b55425 100644
> --- a/arch/powerpc/mm/tlb_hash32.c
> +++ b/arch/powerpc/mm/tlb_hash32.c
> @@ -170,4 +170,5 @@ EXPORT_SYMBOL(flush_tlb_range);
>
>  void __init early_init_mmu(void)
>  {
> +	current_mmu_mode = MMU_MODE_HASH32;
>  }
> diff --git a/arch/powerpc/mm/tlb_nohash.c b/arch/powerpc/mm/tlb_nohash.c
> index 050badc..74300a7 100644
> --- a/arch/powerpc/mm/tlb_nohash.c
> +++ b/arch/powerpc/mm/tlb_nohash.c
> @@ -720,6 +720,7 @@ static void __init early_mmu_set_memory_limit(void)
>  /* boot cpu only */
>  void __init early_init_mmu(void)
>  {
> +	current_mmu_mode = MMU_MODE_NOHASH;
>  	early_init_mmu_global();
>  	early_init_this_mmu();
>  	early_mmu_set_memory_limit();
> @@ -772,6 +773,7 @@ void setup_initial_memory_limit(phys_addr_t first_memblock_base,
>  #else /* ! CONFIG_PPC64 */
>  void __init early_init_mmu(void)
>  {
> +	current_mmu_mode = MMU_MODE_NOHASH32;
>  #ifdef CONFIG_PPC_47x
>  	early_init_mmu_47x();
>  #endif

-aneesh