Re: [PATCH v2] tlb: hugetlb: Add more sizes to tlb_remove_huge_tlb_entry

[Anshuman Khandual <anshuman.khandual@arm.com>]

On 3/30/22 16:55, Steve Capper wrote:
> tlb_remove_huge_tlb_entry only considers PMD_SIZE and PUD_SIZE when
> updating the mmu_gather structure.
> 
> Unfortunately on arm64 there are two additional huge page sizes that
> need to be covered: CONT_PTE_SIZE and CONT_PMD_SIZE. Where an end-user
> attempts to employ contiguous huge pages, a VM_BUG_ON can be experienced
> due to the fact that the tlb structure hasn't been correctly updated by
> the relevant tlb_flush_p.._range() call from tlb_remove_huge_tlb_entry.
> 
> This patch adds inequality logic to the generic implementation of
> tlb_remove_huge_tlb_entry s.t. CONT_PTE_SIZE and CONT_PMD_SIZE are
> effectively covered on arm64. Also, as well as ptes, pmds and puds;
> p4ds are now considered too.
> 
> Reported-by: David Hildenbrand <david@redhat.com>
> Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org>
> Cc: Anshuman Khandual <anshuman.khandual@arm.com>
> Cc: Catalin Marinas <catalin.marinas@arm.com>
> Cc: Will Deacon <will@kernel.org>
> Link: https://lore.kernel.org/linux-mm/811c5c8e-b3a2-85d2-049c-717f17c3a03a@redhat.com/
> Signed-off-by: Steve Capper <steve.capper@arm.com>
> 
> ---
> 
> Changed in V2: instead of doing the per-arch implementation of
> tlb_remove_huge_tlb_entry we add to the generic implmentation, as
> suggested by PeterZ.
> 
> This works well on arm64 with contiguous PTEs/PMDs. Does this look
> reasonable to the ppc folk?

I am wondering whether this should take care of gigantic PGDIR_SIZE
based HugeTLB pages as well ? Although, it will require another new
helper tlb_flush_pgd_range(). Any thoughts ?

> 
> Cheers,
> --
> Steve
> ---
>  include/asm-generic/tlb.h | 10 +++++++---
>  1 file changed, 7 insertions(+), 3 deletions(-)
> 
> diff --git a/include/asm-generic/tlb.h b/include/asm-generic/tlb.h
> index 2c68a545ffa7..71942a1c642d 100644
> --- a/include/asm-generic/tlb.h
> +++ b/include/asm-generic/tlb.h
> @@ -565,10 +565,14 @@ static inline void tlb_flush_p4d_range(struct mmu_gather *tlb,
>  #define tlb_remove_huge_tlb_entry(h, tlb, ptep, address)	\
>  	do {							\
>  		unsigned long _sz = huge_page_size(h);		\
> -		if (_sz == PMD_SIZE)				\
> -			tlb_flush_pmd_range(tlb, address, _sz);	\
> -		else if (_sz == PUD_SIZE)			\
> +		if (_sz >= P4D_SIZE)				\
> +			tlb_flush_p4d_range(tlb, address, _sz);	\
> +		else if (_sz >= PUD_SIZE)			\
>  			tlb_flush_pud_range(tlb, address, _sz);	\
> +		else if (_sz >= PMD_SIZE)			\
> +			tlb_flush_pmd_range(tlb, address, _sz);	\
> +		else						\
> +			tlb_flush_pte_range(tlb, address, _sz);	\
>  		__tlb_remove_tlb_entry(tlb, ptep, address);	\
>  	} while (0)
>