linux-kernel - Re: [PATCH v3 3/5] mmu_notifiers: Call invalidate

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Date:   Fri, 21 Jul 2023 16:27:04 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Alistair Popple <apopple@...dia.com>
Cc:     akpm@...ux-foundation.org, ajd@...ux.ibm.com,
        catalin.marinas@....com, fbarrat@...ux.ibm.com,
        iommu@...ts.linux.dev, jhubbard@...dia.com, kevin.tian@...el.com,
        kvm@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linuxppc-dev@...ts.ozlabs.org, mpe@...erman.id.au,
        nicolinc@...dia.com, npiggin@...il.com, robin.murphy@....com,
        seanjc@...gle.com, will@...nel.org, x86@...nel.org,
        zhi.wang.linux@...il.com, sj@...nel.org
Subject: Re: [PATCH v3 3/5] mmu_notifiers: Call invalidate_range() when
 invalidating TLBs

On Thu, Jul 20, 2023 at 06:39:25PM +1000, Alistair Popple wrote:
> 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
> 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 <apopple@...dia.com>
> Suggested-by: Jason Gunthorpe <jgg@...pe.ca>
> Tested-by: SeongJae Park <sj@...nel.org>
> ---
>  arch/arm64/include/asm/tlbflush.h             | 5 +++++
>  arch/powerpc/include/asm/book3s/64/tlbflush.h | 1 +
>  arch/powerpc/mm/book3s64/radix_hugetlbpage.c  | 1 +
>  arch/powerpc/mm/book3s64/radix_tlb.c          | 6 ++++++
>  arch/x86/include/asm/tlbflush.h               | 2 ++
>  arch/x86/mm/tlb.c                             | 2 ++
>  include/asm-generic/tlb.h                     | 1 -
>  7 files changed, 17 insertions(+), 1 deletion(-)

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

Jason