Re: [PATCH v3 13/13] arm64: mm: Provide level hint for flush_tlb_page()

[Mark Rutland <mark.rutland@arm.com>]

Hi Ryan,

On Mon, Mar 02, 2026 at 01:56:00PM +0000, Ryan Roberts wrote:
> Previously tlb invalidations issued by __flush_tlb_page() did not
> contain a level hint. But the function is clearly only ever targeting
> level 3 tlb entries and its documentation agrees:
> 
>   | this operation only invalidates a single, last-level page-table
>   | entry and therefore does not affect any walk-caches

FWIW, I'd have read "last-level" as synonymous with "leaf" (i.e. a Page
or Block entry, which is the last level of walk) rather than level 3
specifically. The architecture uses the term to match the former (e.g.
in the description of TLBI VALE1IS).

If we're tightening up __flush_tlb_page(), I think it'd be worth either
updating the comment to explicitly note that this only applies to level
3 entries, OR update the comment+name to say it applies to leaf entries,
and have it take a level parameter.

> However, it turns out that the function was actually being used to
> invalidate a level 2 mapping via flush_tlb_fix_spurious_fault_pmd(). 
> The bug was benign because the level hint was not set so the HW would
> still invalidate the PMD mapping, and also because the TLBF_NONOTIFY
> flag was set, the bounds of the mapping were never used for anything
> else.

I suspect (as above) that the current usage was intentional, legitimate
usage, just poorly documented.

> Now that we have the new and improved range-invalidation API, it is
> trival to fix flush_tlb_fix_spurious_fault_pmd() to explicitly flush the
> whole range (locally, without notification and last level only). So
> let's do that, and then update __flush_tlb_page() to hint level 3.

Do we never use __flush_tlb_page() to manipulate a level 1 block
mapping? I'd have expected we did the same lazy invalidation for
permission relazation there, but if that's not the case, then this seems
fine in principle.

> Reviewed-by: Linu Cherian <linu.cherian@arm.com>
> Signed-off-by: Ryan Roberts <ryan.roberts@arm.com>
> ---
>  arch/arm64/include/asm/pgtable.h  | 5 +++--
>  arch/arm64/include/asm/tlbflush.h | 2 +-
>  2 files changed, 4 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index 7039931df4622..b1a96a8f2b17e 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -103,8 +103,9 @@ static inline void arch_leave_lazy_mmu_mode(void)
>  #define flush_tlb_fix_spurious_fault(vma, address, ptep)	\
>  	__flush_tlb_page(vma, address, TLBF_NOBROADCAST | TLBF_NONOTIFY)
>  
> -#define flush_tlb_fix_spurious_fault_pmd(vma, address, pmdp)	\
> -	__flush_tlb_page(vma, address, TLBF_NOBROADCAST | TLBF_NONOTIFY)
> +#define flush_tlb_fix_spurious_fault_pmd(vma, address, pmdp)			\
> +	__flush_tlb_range(vma, address, address + PMD_SIZE, PMD_SIZE, 2,	\
> +			  TLBF_NOBROADCAST | TLBF_NONOTIFY | TLBF_NOWALKCACHE)

Is there a reason to keep __flush_tlb_page(), rather than defining
flush_tlb_fix_spurious_fault() in terms of __flush_tlb_range() with all
the level 3 constants?

Mark.

>  
>  /*
>   * ZERO_PAGE is a global shared page that is always zero: used
> diff --git a/arch/arm64/include/asm/tlbflush.h b/arch/arm64/include/asm/tlbflush.h
> index 5096ec7ab8650..958fe97b744e5 100644
> --- a/arch/arm64/include/asm/tlbflush.h
> +++ b/arch/arm64/include/asm/tlbflush.h
> @@ -591,7 +591,7 @@ static inline void __flush_tlb_page(struct vm_area_struct *vma,
>  	unsigned long start = round_down(uaddr, PAGE_SIZE);
>  	unsigned long end = start + PAGE_SIZE;
>  
> -	__do_flush_tlb_range(vma, start, end, PAGE_SIZE, TLBI_TTL_UNKNOWN,
> +	__do_flush_tlb_range(vma, start, end, PAGE_SIZE, 3,
>  			     TLBF_NOWALKCACHE | flags);
>  }
>  
> -- 
> 2.43.0
>