Subject: Re: [PATCH v2 3/5] mmu_notifiers: Call invalidate_range() when invalidating TLBs

From: Michael Ellerman <[email-masked]>
Date: Tue, 25 Jul 2023 13:41:59 +1000

Alistair Popple <[email-masked]> writes:
> The invalidate_range() is going to become an architecture specific mmu
> notifier used to keep the TLB of secondary MMUs such as an IOMMU in
> sync with the CPU page tables. Currently it is called from separate
> code paths to the main CPU TLB invalidations. This can lead to a
> secondary TLB not getting invalidated when required and makes it hard
> to reason about when exactly the secondary TLB is invalidated.
>
> To fix this move the notifier call to the architecture specific TLB
> maintenance functions for architectures that have secondary MMUs
> requiring explicit software invalidations.
>
> This fixes a SMMU bug on ARM64. On ARM64 PTE permission upgrades
> require a TLB invalidation. This invalidation is done by the
> architecutre specific ptep_set_access_flags() which calls
  ^
  architecture
  
> flush_tlb_page() if required. However this doesn't call the notifier
> resulting in infinite faults being generated by devices using the SMMU
> if it has previously cached a read-only PTE in it's TLB.
>
> Moving the invalidations into the TLB invalidation functions ensures
> all invalidations happen at the same time as the CPU invalidation. The
> architecture specific flush_tlb_all() routines do not call the
> notifier as none of the IOMMUs require this.
>
> Signed-off-by: Alistair Popple <[email-masked]>
> Suggested-by: Jason Gunthorpe <[email-masked]>
> 
...

> diff --git a/arch/powerpc/mm/book3s64/radix_tlb.c b/arch/powerpc/mm/book3s64/radix_tlb.c
> index 0bd4866..9724b26 100644
> --- a/arch/powerpc/mm/book3s64/radix_tlb.c
> +++ b/arch/powerpc/mm/book3s64/radix_tlb.c
> @@ -752,6 +752,8 @@ void radix__local_flush_tlb_page(struct vm_area_struct *vma, unsigned long vmadd
>  		return radix__local_flush_hugetlb_page(vma, vmaddr);
>  #endif
>  	radix__local_flush_tlb_page_psize(vma->vm_mm, vmaddr, mmu_virtual_psize);
> +	mmu_notifier_invalidate_range(vma->vm_mm, vmaddr,
> +						vmaddr + mmu_virtual_psize);
>  }
>  EXPORT_SYMBOL(radix__local_flush_tlb_page);

I think we can skip calling the notifier there? It's explicitly a local flush.

cheers