Re: [PATCH v13 3/3] arm64: Implement page table free interfaces

Will Deacon
2018-06-06T15:44:19Z

On Wed, Jun 06, 2018 at 12:31:21PM +0530, Chintan Pandya wrote:
> arm64 requires break-before-make. Originally, before
> setting up new pmd/pud entry for huge mapping, in few
> cases, the modifying pmd/pud entry was still valid
> and pointing to next level page table as we only
> clear off leaf PTE in unmap leg.
>
> a) This was resulting into stale entry in TLBs (as few
> TLBs also cache intermediate mapping for performance
> reasons)
> b) Also, modifying pmd/pud was the only reference to
> next level page table and it was getting lost without
> freeing it. So, page leaks were happening.
>
> Implement pud_free_pmd_page() and pmd_free_pte_page() to
> enforce BBM and also free the leaking page tables.
>
> Implementation requires,
> 1) Clearing off the current pud/pmd entry
> 2) Invalidation of TLB
> 3) Freeing of the un-used next level page tables
>
> Signed-off-by: Chintan Pandya <cpandya@codeaurora.org>
> ---
> arch/arm64/mm/mmu.c | 48 ++++++++++++++++++++++++++++++++++++++++++++----
> 1 file changed, 44 insertions(+), 4 deletions(-)

Thanks, I think this looks really good now:

Reviewed-by: Will Deacon <will.deacon@arm.com>

Will