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Thu, 01 Aug 2024 11:01:31 -0700 (PDT) Date: Thu, 1 Aug 2024 11:01:30 -0700 In-Reply-To: Mime-Version: 1.0 References: <20240726235234.228822-1-seanjc@google.com> <20240726235234.228822-3-seanjc@google.com> Message-ID: Subject: Re: [PATCH v12 02/84] KVM: arm64: Disallow copying MTE to guest memory while KVM is dirty logging From: Sean Christopherson To: "Aneesh Kumar K.V" Cc: Paolo Bonzini , Marc Zyngier , Oliver Upton , Tianrui Zhao , Bibo Mao , Huacai Chen , Michael Ellerman , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Christian Borntraeger , Janosch Frank , Claudio Imbrenda , kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, loongarch@lists.linux.dev, linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, David Matlack , David Stevens Content-Type: text/plain; charset="us-ascii" X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20240801_110133_432980_2DAF708B X-CRM114-Status: GOOD ( 21.37 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Thu, Aug 01, 2024, Aneesh Kumar K.V wrote: > Sean Christopherson 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 > > --- > > 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 ? No, gfn_to_pfn_prot() == FOLL_GET, kfp->pin == FOLL_PIN. But that's not really relevant. > Should all those pin request fail if kvm->nr_memslots_dirty_logging != 0? No, the conflict with dirty logging is specifically that this code doesn't invoke mark_page_dirty(). And it can't easily do that, because there's no loaded ("running") vCPU, i.e. doing so would trip this WARN: #ifdef CONFIG_HAVE_KVM_DIRTY_RING if (WARN_ON_ONCE(vcpu && vcpu->kvm != kvm)) return; WARN_ON_ONCE(!vcpu && !kvm_arch_allow_write_without_running_vcpu(kvm)); <==== #endif