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SubjectRe: [PATCH v5 3/4] arm64: Implement page table free interfaces
Hi Chintan,

On Tue, Mar 27, 2018 at 06:54:59PM +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>
> ---
> V4->V5:
> - Using __flush_tlb_kernel_pgtable instead of
> flush_tlb_kernel_range
>
>
> arch/arm64/mm/mmu.c | 33 +++++++++++++++++++++++++++++++--
> 1 file changed, 31 insertions(+), 2 deletions(-)
>
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index da98828..3552c7a 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)
> @@ -973,12 +974,40 @@ int pmd_clear_huge(pmd_t *pmdp)
> return 1;
> }
>
> +static int __pmd_free_pte_page(pmd_t *pmd, unsigned long addr, bool tlb_inv)
> +{
> + pmd_t *table;
> +
> + if (pmd_val(*pmd)) {

Please can you follow what I did in 20a004e7b017 ("arm64: mm: Use
READ_ONCE/WRITE_ONCE when accessing page tables") and:

1. Use consistent naming, so pmd_t * pmdp.
2. Use READ_ONCE to dereference the entry once into a local.

Similarly for the pud code below.

> + table = __va(pmd_val(*pmd));
> + pmd_clear(pmd);
> + if (tlb_inv)
> + __flush_tlb_kernel_pgtable(addr);
> +
> + free_page((unsigned long) table);

Hmm. Surely it's only safe to call free_page if !tlb_inv in situations when
the page table is already disconnected at a higher level? That doesn't
appear to be the case with the function below, which still has the pud
installed. What am I missing?

> + }
> + return 1;
> +}
> +
> int pud_free_pmd_page(pud_t *pud, unsigned long addr)
> {
> - return pud_none(*pud);
> + pmd_t *table;
> + int i;
> +
> + if (pud_val(*pud)) {
> + table = __va(pud_val(*pud));
> + for (i = 0; i < PTRS_PER_PMD; i++)
> + __pmd_free_pte_page(&table[i], addr + (i * PMD_SIZE),
> + false);
> +
> + pud_clear(pud);
> + flush_tlb_kernel_range(addr, addr + PUD_SIZE);

Why aren't you using __flush_tlb_kernel_pgtable here?

Will

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