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SubjectRe: [PATCH v3 2/3] arm64: Implement page table free interfaces
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On 3/20/2018 12:59 AM, Kani, Toshi wrote:
> On Mon, 2018-03-19 at 18:10 +0530, Chintan Pandya wrote:
>> Implement pud_free_pmd_page() and pmd_free_pte_page().
>>
>> Implementation requires,
>> 1) Freeing of the un-used next level page tables
>> 2) Clearing off the current pud/pmd entry
>> 3) Invalidate TLB which could have previously
>> valid but not stale entry
>>
>> Signed-off-by: Chintan Pandya <cpandya@codeaurora.org>
>> ---
>> arch/arm64/mm/mmu.c | 30 ++++++++++++++++++++++++++++--
>> 1 file changed, 28 insertions(+), 2 deletions(-)
>>
>> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
>> index da98828..c70f139 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)
>> @@ -975,10 +976,35 @@ int pmd_clear_huge(pmd_t *pmdp)
>>
>> int pud_free_pmd_page(pud_t *pud, unsigned long addr)
>> {
>> - return pud_none(*pud);
>> + pmd_t *pmd;
>> + int i;
>> +
>> + pmd = __va(pud_val(*pud));
>> + if (pud_val(*pud)) {
>> + for (i = 0; i < PTRS_PER_PMD; i++)
>> + pmd_free_pte_page(&pmd[i], addr + (i * PMD_SIZE));
>> +
>> + free_page((unsigned long) pmd);
>
> Why do you want to free this pmd page before clearing the pud entry on
> this arm64 version (as it seems you intentionally changed it from the
> x86 version)? It can be reused while being pointed by the pud. Same
> for pmd.
Noted.
>
>> + pud_clear(pud);
>> + flush_tlb_kernel_range(addr, addr + PUD_SIZE);
>
> Since you purge the entire pud range here, do you still need to call
> pmd_free_pte_page() to purge each pmd range? This looks very expensive.
> You may want to consider if calling internal __pmd_free_pte_page()
> without the purge operation works.
I completely missed that. Sure, will fix this.

I will upload v4 fixing all 4 comments.
>
> -Toshi
>

Chintan
--
Qualcomm India Private Limited, on behalf of Qualcomm Innovation Center,
Inc. is a member of the Code Aurora Forum, a Linux Foundation
Collaborative Project

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