Re: [PATCH v12 4/5] arm64: Implement page table free interfaces

Will Deacon
2018-06-04T12:12:59Z

On Fri, Jun 01, 2018 at 06:09:17PM +0530, Chintan Pandya wrote:
> Implement pud_free_pmd_page() and pmd_free_pte_page().
>
> Implementation requires,
> 1) Clearing off the current pud/pmd entry
> 2) Invalidate TLB which could have previously
> valid but not stale entry
> 3) Freeing of the un-used next level page tables

Please can you rewrite this describing the problem that you're solving,
rather than a brief summary of some requirements?

> Signed-off-by: Chintan Pandya <cpandya@codeaurora.org>
> ---
> arch/arm64/mm/mmu.c | 38 ++++++++++++++++++++++++++++++++++----
> 1 file changed, 34 insertions(+), 4 deletions(-)
>
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 8ae5d7a..6e7e16c 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -45,6 +45,7 @@
> #include <asm/memblock.h>
> #include <asm/mmu_context.h>
> #include <asm/ptdump.h>
> +#include <asm/tlbflush.h>
>
> #define NO_BLOCK_MAPPINGS BIT(0)
> #define NO_CONT_MAPPINGS BIT(1)
> @@ -977,12 +978,41 @@ int pmd_clear_huge(pmd_t *pmdp)
> return 1;
> }
>
> -int pud_free_pmd_page(pud_t *pud, unsigned long addr)
> +int pmd_free_pte_page(pmd_t *pmdp, unsigned long addr)
> {
> - return pud_none(*pud);
> + pte_t *table;
> + pmd_t pmd;
> +
> + pmd = READ_ONCE(*pmdp);
> + if (pmd_present(pmd)) {
> + table = pmd_page_vaddr(pmd);
> + pmd_clear(pmdp);
> + __flush_tlb_kernel_pgtable(addr);
> + pte_free_kernel(NULL, table);
> + }
> + return 1;
> }
>
> -int pmd_free_pte_page(pmd_t *pmd, unsigned long addr)
> +int pud_free_pmd_page(pud_t *pudp, unsigned long addr)
> {
> - return pmd_none(*pmd);
> + pmd_t *table;
> + pmd_t *entry;
> + pud_t pud;
> + unsigned long next, end;
> +
> + pud = READ_ONCE(*pudp);
> + if (pud_present(pud)) {

Just some stylistic stuff, but please can you rewrite this as:

if (!pud_present(pud) || VM_WARN_ON(!pud_table(pud)))
return 1;

similarly for the pmd/pte code above.

> + table = pud_page_vaddr(pud);
> + entry = table;

Could you rename entry -> pmdp, please?

> + next = addr;
> + end = addr + PUD_SIZE;
> + do {
> + pmd_free_pte_page(entry, next);
> + } while (entry++, next += PMD_SIZE, next != end);
> +
> + pud_clear(pudp);
> + __flush_tlb_kernel_pgtable(addr);
> + pmd_free(NULL, table);
> + }
> + return 1;

So with these patches, we only ever return 1 from these helpers. It looks
like the same is true for x86, so how about we make them void and move the
calls inside the conditionals in lib/ioremap.c? Obviously, this would be a
separate patch on the end.

Will