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[35.185.214.157]) by smtp.gmail.com with ESMTPSA id b18sm255135pfl.24.2021.10.19.15.38.08 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 19 Oct 2021 15:38:08 -0700 (PDT) Date: Tue, 19 Oct 2021 22:38:04 +0000 From: Sean Christopherson To: "Maciej S. Szmigiero" Cc: Paolo Bonzini , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Igor Mammedov , Marc Zyngier , James Morse , Julien Thierry , Suzuki K Poulose , Huacai Chen , Aleksandar Markovic , Paul Mackerras , Christian Borntraeger , Janosch Frank , David Hildenbrand , Cornelia Huck , Claudio Imbrenda , Joerg Roedel , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v5 04/13] KVM: x86: Move n_memslots_pages recalc to kvm_arch_prepare_memory_region() Message-ID: References: <2a4ceee16546deeab7090efea2ee9c0db5444b84.1632171479.git.maciej.szmigiero@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <2a4ceee16546deeab7090efea2ee9c0db5444b84.1632171479.git.maciej.szmigiero@oracle.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Sep 20, 2021, Maciej S. Szmigiero wrote: > From: "Maciej S. Szmigiero" > > This allows us to return a proper error code in case we spot an underflow. > > Signed-off-by: Maciej S. Szmigiero > --- > arch/x86/kvm/x86.c | 49 ++++++++++++++++++++++++++-------------------- > 1 file changed, 28 insertions(+), 21 deletions(-) > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 97d86223427d..0fffb8414009 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -11511,9 +11511,23 @@ int kvm_arch_prepare_memory_region(struct kvm *kvm, > const struct kvm_userspace_memory_region *mem, > enum kvm_mr_change change) > { > - if (change == KVM_MR_CREATE || change == KVM_MR_MOVE) > - return kvm_alloc_memslot_metadata(kvm, new, > - mem->memory_size >> PAGE_SHIFT); > + if (change == KVM_MR_CREATE || change == KVM_MR_MOVE) { > + int ret; > + > + ret = kvm_alloc_memslot_metadata(kvm, new, > + mem->memory_size >> PAGE_SHIFT); > + if (ret) > + return ret; > + > + if (change == KVM_MR_CREATE) > + kvm->arch.n_memslots_pages += new->npages; > + } else if (change == KVM_MR_DELETE) { > + if (WARN_ON(kvm->arch.n_memslots_pages < old->npages)) > + return -EIO; This is not worth the churn. In a way, it's worse because userspace can spam the living snot out of the kernel log by retrying the ioctl(). Since underflow can happen if and only if there's a KVM bug, and a pretty bad one at that, just make the original WARN_ON a KVM_BUG_ON. That will kill the VM and also provide the WARN_ON_ONCE behavior that we probably want. > + > + kvm->arch.n_memslots_pages -= old->npages; > + } > + > return 0; > } >