Re: [RFC PATCH v0 5/5] powerpc/mm/radix: Remove split_kernel_mapping()

["Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>]

Bharata B Rao <bharata@linux.ibm.com> writes:

> With hot-plugged memory getting mapped with 2M mappings always,
> there will be no need to split any mappings during unplug.
>
> Hence remove split_kernel_mapping() and associated code. This
> essentially is a revert of
> commit 4dd5f8a99e791 ("powerpc/mm/radix: Split linear mapping on hot-unplug")
>

Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>

> Signed-off-by: Bharata B Rao <bharata@linux.ibm.com>
> ---
>  arch/powerpc/mm/book3s64/radix_pgtable.c | 93 +++++-------------------
>  1 file changed, 19 insertions(+), 74 deletions(-)
>
> diff --git a/arch/powerpc/mm/book3s64/radix_pgtable.c b/arch/powerpc/mm/book3s64/radix_pgtable.c
> index 0d9ef3277579..56f2c698deac 100644
> --- a/arch/powerpc/mm/book3s64/radix_pgtable.c
> +++ b/arch/powerpc/mm/book3s64/radix_pgtable.c
> @@ -15,7 +15,6 @@
>  #include <linux/mm.h>
>  #include <linux/hugetlb.h>
>  #include <linux/string_helpers.h>
> -#include <linux/stop_machine.h>
>  #include <linux/memory.h>
>  
>  #include <asm/pgtable.h>
> @@ -782,30 +781,6 @@ static void free_pud_table(pud_t *pud_start, pgd_t *pgd)
>  	pgd_clear(pgd);
>  }
>  
> -struct change_mapping_params {
> -	pte_t *pte;
> -	unsigned long start;
> -	unsigned long end;
> -	unsigned long aligned_start;
> -	unsigned long aligned_end;
> -};
> -
> -static int __meminit stop_machine_change_mapping(void *data)
> -{
> -	struct change_mapping_params *params =
> -			(struct change_mapping_params *)data;
> -
> -	if (!data)
> -		return -1;
> -
> -	spin_unlock(&init_mm.page_table_lock);
> -	pte_clear(&init_mm, params->aligned_start, params->pte);
> -	create_physical_mapping(__pa(params->aligned_start), __pa(params->start), -1);
> -	create_physical_mapping(__pa(params->end), __pa(params->aligned_end), -1);
> -	spin_lock(&init_mm.page_table_lock);
> -	return 0;
> -}
> -
>  static void remove_pte_table(pte_t *pte_start, unsigned long addr,
>  			     unsigned long end)
>  {
> @@ -834,52 +809,6 @@ static void remove_pte_table(pte_t *pte_start, unsigned long addr,
>  	}
>  }
>  
> -/*
> - * clear the pte and potentially split the mapping helper
> - */
> -static void __meminit split_kernel_mapping(unsigned long addr, unsigned long end,
> -				unsigned long size, pte_t *pte)
> -{
> -	unsigned long mask = ~(size - 1);
> -	unsigned long aligned_start = addr & mask;
> -	unsigned long aligned_end = addr + size;
> -	struct change_mapping_params params;
> -	bool split_region = false;
> -
> -	if ((end - addr) < size) {
> -		/*
> -		 * We're going to clear the PTE, but not flushed
> -		 * the mapping, time to remap and flush. The
> -		 * effects if visible outside the processor or
> -		 * if we are running in code close to the
> -		 * mapping we cleared, we are in trouble.
> -		 */
> -		if (overlaps_kernel_text(aligned_start, addr) ||
> -			overlaps_kernel_text(end, aligned_end)) {
> -			/*
> -			 * Hack, just return, don't pte_clear
> -			 */
> -			WARN_ONCE(1, "Linear mapping %lx->%lx overlaps kernel "
> -				  "text, not splitting\n", addr, end);
> -			return;
> -		}
> -		split_region = true;
> -	}
> -
> -	if (split_region) {
> -		params.pte = pte;
> -		params.start = addr;
> -		params.end = end;
> -		params.aligned_start = addr & ~(size - 1);
> -		params.aligned_end = min_t(unsigned long, aligned_end,
> -				(unsigned long)__va(memblock_end_of_DRAM()));
> -		stop_machine(stop_machine_change_mapping, &params, NULL);
> -		return;
> -	}
> -
> -	pte_clear(&init_mm, addr, pte);
> -}
> -
>  static void remove_pmd_table(pmd_t *pmd_start, unsigned long addr,
>  			     unsigned long end)
>  {
> @@ -895,7 +824,12 @@ static void remove_pmd_table(pmd_t *pmd_start, unsigned long addr,
>  			continue;
>  
>  		if (pmd_is_leaf(*pmd)) {
> -			split_kernel_mapping(addr, end, PMD_SIZE, (pte_t *)pmd);
> +			if (!IS_ALIGNED(addr, PMD_SIZE) ||
> +			    !IS_ALIGNED(next, PMD_SIZE)) {
> +				WARN_ONCE(1, "%s: unaligned range\n", __func__);
> +				continue;
> +			}
> +			pte_clear(&init_mm, addr, (pte_t *)pmd);
>  			continue;
>  		}
>  
> @@ -920,7 +854,12 @@ static void remove_pud_table(pud_t *pud_start, unsigned long addr,
>  			continue;
>  
>  		if (pud_is_leaf(*pud)) {
> -			split_kernel_mapping(addr, end, PUD_SIZE, (pte_t *)pud);
> +			if (!IS_ALIGNED(addr, PUD_SIZE) ||
> +			    !IS_ALIGNED(next, PUD_SIZE)) {
> +				WARN_ONCE(1, "%s: unaligned range\n", __func__);
> +				continue;
> +			}
> +			pte_clear(&init_mm, addr, (pte_t *)pud);
>  			continue;
>  		}
>  
> @@ -946,7 +885,13 @@ static void __meminit remove_pagetable(unsigned long start, unsigned long end)
>  			continue;
>  
>  		if (pgd_is_leaf(*pgd)) {
> -			split_kernel_mapping(addr, end, PGDIR_SIZE, (pte_t *)pgd);
> +			if (!IS_ALIGNED(addr, PGDIR_SIZE) ||
> +			    !IS_ALIGNED(next, PGDIR_SIZE)) {
> +				WARN_ONCE(1, "%s: unaligned range\n", __func__);
> +				continue;
> +			}
> +
> +			pte_clear(&init_mm, addr, (pte_t *)pgd);
>  			continue;
>  		}
>  
> -- 
> 2.21.0