Re: [PATCH] arm64: tlb: Flush walk cache when unsharing PMD tables

[Catalin Marinas <catalin.marinas@arm.com>]

+ David H.

On Thu, May 21, 2026 at 03:30:11PM +0800, Zeng Heng wrote:
> From: Zeng Heng <zengheng4@huawei.com>
> 
> When huge_pmd_unshare() is called to unshare a PMD table, the
> tlb_unshare_pmd_ptdesc() function sets tlb->unshared_tables=true
> but the aarch64 tlb_flush() only checked tlb->freed_tables to
> determine whether to use TLBF_NONE (vae1is, invalidates walk
> cache) or TLBF_NOWALKCACHE (vale1is, leaf-only).
> 
> This caused the stale PMD page table entry to remain in the walk cache
> after unshare, potentially leading to incorrect page table walks.
> 
> Fix by including unshared_tables in the check, so that when
> unsharing tables, TLBF_NONE is used and the walk cache is properly
> invalidated.
> 
> Here is the detailed distinction between vae1is and vale1is:
> 
> | Instruction Combination  | Actual Invalidation Scope                         |
> | ------------------------ | --------------------------------------------------|
> | `VAE1IS`  + TTL=`0`      | All entries at all levels (full invalidation)     |
> | `VAE1IS`  + TTL=`2` (L2) | Non-leaf at Level 0/1 + leaf at Level 2           |
> | `VALE1IS` + TTL=`0`      | Leaf entries at all levels (non-leaf not cleared) |
> | `VALE1IS` + TTL=`2` (L2) | Leaf entry at Level 2 only                        |
> 
> Signed-off-by: Zeng Heng <zengheng4@huawei.com>

The fix looks fine but does it need:

Fixes: 8ce720d5bd91 ("mm/hugetlb: fix excessive IPI broadcasts when unsharing PMD tables using mmu_gather")
Cc: <stable@vger.kernel.org>

> ---
>  arch/arm64/include/asm/tlb.h | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm64/include/asm/tlb.h b/arch/arm64/include/asm/tlb.h
> index 10869d7731b8..751bd57bc3ba 100644
> --- a/arch/arm64/include/asm/tlb.h
> +++ b/arch/arm64/include/asm/tlb.h
> @@ -53,7 +53,8 @@ static inline int tlb_get_level(struct mmu_gather *tlb)
>  static inline void tlb_flush(struct mmu_gather *tlb)
>  {
>  	struct vm_area_struct vma = TLB_FLUSH_VMA(tlb->mm, 0);
> -	tlbf_t flags = tlb->freed_tables ? TLBF_NONE : TLBF_NOWALKCACHE;
> +	tlbf_t flags = (tlb->freed_tables || tlb->unshared_tables) ?
> +			TLBF_NONE : TLBF_NOWALKCACHE;
>  	unsigned long stride = tlb_get_unmap_size(tlb);
>  	int tlb_level = tlb_get_level(tlb);
>  
> -- 
> 2.43.0

-- 
Catalin