Subject: Re: [PATCH v4 3/4] powerpc/mm: add radix__remove_section_mapping()

From: "Aneesh Kumar K.V" <[email-masked]>
Date: Wed, 04 Jan 2017 10:37:58 +0530

Reza Arbab <[email-masked]> writes:

> Tear down and free the four-level page tables of physical mappings
> during memory hotremove.
>
> Borrow the basic structure of remove_pagetable() and friends from the
> identically-named x86 functions. Simplify things a bit so locking and
> tlb flushing are only done in the outermost function.
>
> Memory must be offline to be removed, thus not in use. So there
> shouldn't be the sort of concurrent page walking activity here that
> might prompt us to use RCU.
>
> Signed-off-by: Reza Arbab <[email-masked]>
> ---
>  arch/powerpc/include/asm/book3s/64/radix.h |   1 +
>  arch/powerpc/mm/pgtable-book3s64.c         |   2 +-
>  arch/powerpc/mm/pgtable-radix.c            | 149 +++++++++++++++++++++++++++++
>  3 files changed, 151 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/include/asm/book3s/64/radix.h b/arch/powerpc/include/asm/book3s/64/radix.h
> index 43c2571..0032b66 100644
> --- a/arch/powerpc/include/asm/book3s/64/radix.h
> +++ b/arch/powerpc/include/asm/book3s/64/radix.h
> @@ -294,6 +294,7 @@ static inline unsigned long radix__get_tree_size(void)
>
>  #ifdef CONFIG_MEMORY_HOTPLUG
>  int radix__create_section_mapping(unsigned long start, unsigned long end);
> +int radix__remove_section_mapping(unsigned long start, unsigned long end);
>  #endif /* CONFIG_MEMORY_HOTPLUG */
>  #endif /* __ASSEMBLY__ */
>  #endif
> diff --git a/arch/powerpc/mm/pgtable-book3s64.c b/arch/powerpc/mm/pgtable-book3s64.c
> index 2b13f6b..b798ff6 100644
> --- a/arch/powerpc/mm/pgtable-book3s64.c
> +++ b/arch/powerpc/mm/pgtable-book3s64.c
> @@ -139,7 +139,7 @@ int create_section_mapping(unsigned long start, unsigned long end)
>  int remove_section_mapping(unsigned long start, unsigned long end)
>  {
>  	if (radix_enabled())
> -		return -ENODEV;
> +		return radix__remove_section_mapping(start, end);
>
>  	return hash__remove_section_mapping(start, end);
>  }
> diff --git a/arch/powerpc/mm/pgtable-radix.c b/arch/powerpc/mm/pgtable-radix.c
> index 3588895..f7a8e625 100644
> --- a/arch/powerpc/mm/pgtable-radix.c
> +++ b/arch/powerpc/mm/pgtable-radix.c
> @@ -457,10 +457,159 @@ void radix__setup_initial_memory_limit(phys_addr_t first_memblock_base,
>  }
>
>  #ifdef CONFIG_MEMORY_HOTPLUG
> +static void free_pte_table(pte_t *pte_start, pmd_t *pmd)
> +{
> +	pte_t *pte;
> +	int i;
> +
> +	for (i = 0; i < PTRS_PER_PTE; i++) {
> +		pte = pte_start + i;
> +		if (!pte_none(*pte))
> +			return;
> +	}
> +
> +	pte_free_kernel(&init_mm, pte_start);
> +	pmd_clear(pmd);
> +}
> +
> +static void free_pmd_table(pmd_t *pmd_start, pud_t *pud)
> +{
> +	pmd_t *pmd;
> +	int i;
> +
> +	for (i = 0; i < PTRS_PER_PMD; i++) {
> +		pmd = pmd_start + i;
> +		if (!pmd_none(*pmd))
> +			return;
> +	}
> +
> +	pmd_free(&init_mm, pmd_start);
> +	pud_clear(pud);
> +}
> +
> +static void free_pud_table(pud_t *pud_start, pgd_t *pgd)
> +{
> +	pud_t *pud;
> +	int i;
> +
> +	for (i = 0; i < PTRS_PER_PUD; i++) {
> +		pud = pud_start + i;
> +		if (!pud_none(*pud))
> +			return;
> +	}
> +
> +	pud_free(&init_mm, pud_start);
> +	pgd_clear(pgd);
> +}
> +
> +static void remove_pte_table(pte_t *pte_start, unsigned long addr,
> +			     unsigned long end)
> +{
> +	unsigned long next;
> +	pte_t *pte;
> +
> +	pte = pte_start + pte_index(addr);
> +	for (; addr < end; addr = next, pte++) {
> +		next = (addr + PAGE_SIZE) & PAGE_MASK;
> +		if (next > end)
> +			next = end;
> +
> +		if (!pte_present(*pte))
> +			continue;
> +
> +		pte_clear(&init_mm, addr, pte);
> +	}
> +}
> +
> +static void remove_pmd_table(pmd_t *pmd_start, unsigned long addr,
> +			     unsigned long end)
> +{
> +	unsigned long next;
> +	pte_t *pte_base;
> +	pmd_t *pmd;
> +
> +	pmd = pmd_start + pmd_index(addr);
> +	for (; addr < end; addr = next, pmd++) {
> +		next = pmd_addr_end(addr, end);
> +
> +		if (!pmd_present(*pmd))
> +			continue;
> +
> +		if (pmd_huge(*pmd)) {
> +			pte_clear(&init_mm, addr, (pte_t *)pmd);
> +			continue;
> +		}
> +
> +		pte_base = (pte_t *)pmd_page_vaddr(*pmd);
> +		remove_pte_table(pte_base, addr, next);
> +		free_pte_table(pte_base, pmd);
> +	}
> +}
> +
> +static void remove_pud_table(pud_t *pud_start, unsigned long addr,
> +			     unsigned long end)
> +{
> +	unsigned long next;
> +	pmd_t *pmd_base;
> +	pud_t *pud;
> +
> +	pud = pud_start + pud_index(addr);
> +	for (; addr < end; addr = next, pud++) {
> +		next = pud_addr_end(addr, end);
> +
> +		if (!pud_present(*pud))
> +			continue;
> +
> +		if (pud_huge(*pud)) {
> +			pte_clear(&init_mm, addr, (pte_t *)pud);
> +			continue;
> +		}
> +
> +		pmd_base = (pmd_t *)pud_page_vaddr(*pud);
> +		remove_pmd_table(pmd_base, addr, next);
> +		free_pmd_table(pmd_base, pud);
> +	}
> +}
> +
> +static void remove_pagetable(unsigned long start, unsigned long end)
> +{
> +	unsigned long addr, next;
> +	pud_t *pud_base;
> +	pgd_t *pgd;
> +
> +	spin_lock(&init_mm.page_table_lock);
> +
> +	for (addr = start; addr < end; addr = next) {
> +		next = pgd_addr_end(addr, end);
> +
> +		pgd = pgd_offset_k(addr);
> +		if (!pgd_present(*pgd))
> +			continue;
> +
> +		if (pgd_huge(*pgd)) {
> +			pte_clear(&init_mm, addr, (pte_t *)pgd);
> +			continue;
> +		}
> +
> +		pud_base = (pud_t *)pgd_page_vaddr(*pgd);
> +		remove_pud_table(pud_base, addr, next);
> +		free_pud_table(pud_base, pgd);
> +	}
> +
> +	spin_unlock(&init_mm.page_table_lock);

What is this lock protecting ?

> +	flush_tlb_kernel_range(start, end);

We can use radix__flush_tlb_kernel_range avoiding an if
(radix_enabled()) conditional ? Also if needed we could make all the
above take a radix__ prefix ?

> +}
> +
>  int __ref radix__create_section_mapping(unsigned long start, unsigned long end)
>  {
>  	return create_physical_mapping(start, end);
>  }
> +
> +int radix__remove_section_mapping(unsigned long start, unsigned long end)
> +{
> +	remove_pagetable(start, end);
> +	return 0;
> +}
>  #endif /* CONFIG_MEMORY_HOTPLUG */
>
>  #ifdef CONFIG_SPARSEMEM_VMEMMAP
> -- 
> 1.8.3.1