linux-kernel - Re: [PATCH v12 02/84] KVM: arm64: Disallow copying MTE to guest memory while KVM is dirty logging

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Message-ID: <yq5aikwku25o.fsf@kernel.org>
Date: Thu, 01 Aug 2024 13:04:43 +0530
From: Aneesh Kumar K.V <aneesh.kumar@...nel.org>
To: Sean Christopherson <seanjc@...gle.com>,
	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>,
	Sean Christopherson <seanjc@...gle.com>
Cc: 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

Sean Christopherson <seanjc@...gle.com> writes:

> 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;
> +	}
> +
>

is this equivalent to kvm_follow_pfn() with kfp->pin = 1 ? Should all
those pin request fail if kvm->nr_memslots_dirty_logging != 0? 


>  	while (length > 0) {
>  		kvm_pfn_t pfn = gfn_to_pfn_prot(kvm, gfn, write, NULL);
>  		void *maddr;
> -- 
> 2.46.0.rc1.232.g9752f9e123-goog