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Message-ID: <ZrOfB8bOdSJVcWFr@arm.com>
Date: Wed, 7 Aug 2024 17:21:27 +0100
From: Catalin Marinas <catalin.marinas@....com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, Marc Zyngier <maz@...nel.org>,
Oliver Upton <oliver.upton@...ux.dev>,
Tianrui Zhao <zhaotianrui@...ngson.cn>,
Bibo Mao <maobibo@...ngson.cn>, Huacai Chen <chenhuacai@...nel.org>,
Michael Ellerman <mpe@...erman.id.au>,
Anup Patel <anup@...infault.org>,
Paul Walmsley <paul.walmsley@...ive.com>,
Palmer Dabbelt <palmer@...belt.com>,
Albert Ou <aou@...s.berkeley.edu>,
Christian Borntraeger <borntraeger@...ux.ibm.com>,
Janosch Frank <frankja@...ux.ibm.com>,
Claudio Imbrenda <imbrenda@...ux.ibm.com>, kvm@...r.kernel.org,
linux-arm-kernel@...ts.infradead.org, kvmarm@...ts.linux.dev,
loongarch@...ts.linux.dev, linux-mips@...r.kernel.org,
linuxppc-dev@...ts.ozlabs.org, kvm-riscv@...ts.infradead.org,
linux-riscv@...ts.infradead.org, linux-kernel@...r.kernel.org,
David Matlack <dmatlack@...gle.com>,
David Stevens <stevensd@...omium.org>
Subject: Re: [PATCH v12 02/84] KVM: arm64: Disallow copying MTE to guest
memory while KVM is dirty logging
On Fri, Jul 26, 2024 at 04:51:11PM -0700, Sean Christopherson wrote:
> Disallow copying MTE tags to guest memory while KVM is dirty logging, as
> writing guest memory without marking the gfn as dirty in the memslot could
> result in userspace failing to migrate the updated page. Ideally (maybe?),
> KVM would simply mark the gfn as dirty, but there is no vCPU to work with,
> and presumably the only use case for copy MTE tags _to_ the guest is when
> restoring state on the target.
>
> Fixes: f0376edb1ddc ("KVM: arm64: Add ioctl to fetch/store tags in a guest")
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
> ---
> arch/arm64/kvm/guest.c | 5 +++++
> 1 file changed, 5 insertions(+)
>
> diff --git a/arch/arm64/kvm/guest.c b/arch/arm64/kvm/guest.c
> index e1f0ff08836a..962f985977c2 100644
> --- a/arch/arm64/kvm/guest.c
> +++ b/arch/arm64/kvm/guest.c
> @@ -1045,6 +1045,11 @@ int kvm_vm_ioctl_mte_copy_tags(struct kvm *kvm,
>
> mutex_lock(&kvm->slots_lock);
>
> + if (write && atomic_read(&kvm->nr_memslots_dirty_logging)) {
> + ret = -EBUSY;
> + goto out;
> + }
There are ways to actually log the page dirtying but I don't think
it's worth it. AFAICT, reading the tags still works and that's what's
used during migration (on the VM where dirty tracking takes place).
Reviewed-by: Catalin Marinas <catalin.marinas@....com>
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