Re: [PATCH v3 6/7] KVM: arm64: permit all VM_MTE_ALLOWED mappings with MTE enabled

From: Peter Collingbourne <pcc@google.com>
To: Marc Zyngier <maz@kernel.org>
Cc: Linux ARM <linux-arm-kernel@lists.infradead.org>,
	kvmarm@lists.cs.columbia.edu,  Cornelia Huck <cohuck@redhat.com>,
	Catalin Marinas <catalin.marinas@arm.com>,
	 Will Deacon <will@kernel.org>,
	Evgenii Stepanov <eugenis@google.com>,
	kvm@vger.kernel.org,  Steven Price <steven.price@arm.com>,
	Vincenzo Frascino <vincenzo.frascino@arm.com>
Subject: Re: [PATCH v3 6/7] KVM: arm64: permit all VM_MTE_ALLOWED mappings with MTE enabled
Date: Mon, 12 Sep 2022 21:10:59 -0700	[thread overview]
Message-ID: <CAMn1gO6ZHrQkkYOaicDftUbRSYgngUa4bPKFTLk_q0qxuGz6Zw@mail.gmail.com> (raw)
In-Reply-To: <874jxcv9xn.wl-maz@kernel.org>

On Mon, Sep 12, 2022 at 9:23 AM Marc Zyngier <maz@kernel.org> wrote:
>
> On Wed, 10 Aug 2022 20:30:32 +0100,
> Peter Collingbourne <pcc@google.com> wrote:
> >
> > Certain VMMs such as crosvm have features (e.g. sandboxing) that depend
> > on being able to map guest memory as MAP_SHARED. The current restriction
> > on sharing MAP_SHARED pages with the guest is preventing the use of
> > those features with MTE. Now that the races between tasks concurrently
> > clearing tags on the same page have been fixed, remove this restriction.
> >
> > Signed-off-by: Peter Collingbourne <pcc@google.com>
> > ---
> >  arch/arm64/kvm/mmu.c | 8 --------
> >  1 file changed, 8 deletions(-)
> >
> > diff --git a/arch/arm64/kvm/mmu.c b/arch/arm64/kvm/mmu.c
> > index d54be80e31dd..fc65dc20655d 100644
> > --- a/arch/arm64/kvm/mmu.c
> > +++ b/arch/arm64/kvm/mmu.c
> > @@ -1075,14 +1075,6 @@ static void sanitise_mte_tags(struct kvm *kvm, kvm_pfn_t pfn,
> >
> >  static bool kvm_vma_mte_allowed(struct vm_area_struct *vma)
> >  {
> > -     /*
> > -      * VM_SHARED mappings are not allowed with MTE to avoid races
> > -      * when updating the PG_mte_tagged page flag, see
> > -      * sanitise_mte_tags for more details.
> > -      */
> > -     if (vma->vm_flags & VM_SHARED)
> > -             return false;
> > -
> >       return vma->vm_flags & VM_MTE_ALLOWED;
> >  }
> >
>
> Can you provide a pointer to some VMM making use of this functionality
> and enabling MTE? A set of crosvm patches (for example) would be
> useful to evaluate this series.

Hi Marc,

I've been using a modified crosvm to test this series. Please find
below a link to the proposed crosvm patches which make use of the
series:
https://chromium-review.googlesource.com/c/crosvm/crosvm/+/3892141

Peter

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