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

Chintan Pandya
2018-06-04T13:43:25Z

On 6/4/2018 5:43 PM, Will Deacon wrote:
> 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?

Okay. I'll fix this in v13.

>
>> 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.

Okay. v13 will have this.

>
>> + table = pud_page_vaddr(pud);
>> + entry = table;
>
> Could you rename entry -> pmdp, please?

Sure.

>
>> + 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.

That sounds valid code churn to me. But since x86 discussion is not
concluded yet, I would wait to share until that gets resolved. May be
not in v13 but separate effort. Would that be okay to you ?

>
> Will
>

Chintan
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