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

[Zeng Heng]

Hi Catalin,

On 2026/5/21 23:05, Catalin Marinas wrote:
> + David H.
>
> On Thu, May 21, 2026 at 03:30:11PM +0800, Zeng Heng wrote:
>> From: Zeng Heng <zengheng4 at 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 at 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 at vger.kernel.org>

It makes sense to me. Thanks a lot for that.


Best regards,
Zeng Heng

>> ---
>>   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