linux-kernel - Re: [PATCH 3/4] mmu_notifiers: Call arch_invalidate_secondary

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Date:   Tue, 18 Jul 2023 15:29:26 -0300
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Alistair Popple <apopple@...dia.com>, 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
Subject: Re: [PATCH 3/4] mmu_notifiers: Call arch_invalidate_secondary_tlbs()
 when invalidating TLBs

On Tue, Jul 18, 2023 at 11:17:59AM -0700, Andrew Morton wrote:
> On Tue, 18 Jul 2023 17:56:17 +1000 Alistair Popple <apopple@...dia.com> wrote:
> 
> > The arch_invalidate_secondary_tlbs() is 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.
> 
> This sounds like a pretty serious bug.  Can it happen in current
> released kernels?  If so, is a -stable backport needed?

There are currently no in-kernel drivers using the IOMMU SVA API, so
the impact for -stable is sort of muted. But it is serious if you are
unlucky to hit it.

Jason