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[35.185.214.157]) by smtp.gmail.com with ESMTPSA id h2sm4707798pjk.44.2021.11.04.15.41.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 04 Nov 2021 15:41:57 -0700 (PDT) Date: Thu, 4 Nov 2021 22:41:53 +0000 From: Sean Christopherson To: Ben Gardon Cc: Marc Zyngier , Huacai Chen , Aleksandar Markovic , Paul Mackerras , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , Christian Borntraeger , Janosch Frank , Paolo Bonzini , James Morse , Alexandru Elisei , Suzuki K Poulose , Atish Patra , David Hildenbrand , Cornelia Huck , Claudio Imbrenda , Vitaly Kuznetsov , Wanpeng Li , Jim Mattson , Joerg Roedel , linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, linux-mips@vger.kernel.org, kvm@vger.kernel.org, kvm-ppc@vger.kernel.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, "Maciej S . Szmigiero" Subject: Re: [PATCH v5.5 01/30] KVM: Ensure local memslot copies operate on up-to-date arch-specific data Message-ID: References: <20211104002531.1176691-1-seanjc@google.com> <20211104002531.1176691-2-seanjc@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Nov 04, 2021, Ben Gardon wrote: > > @@ -1597,6 +1596,26 @@ static int kvm_set_memslot(struct kvm *kvm, > > kvm_copy_memslots(slots, __kvm_memslots(kvm, as_id)); > > } > > > > + /* > > + * Make a full copy of the old memslot, the pointer will become stale > > + * when the memslots are re-sorted by update_memslots(), and the old > > + * memslot needs to be referenced after calling update_memslots(), e.g. > > + * to free its resources and for arch specific behavior. This needs to > > + * happen *after* (re)acquiring slots_arch_lock. > > + */ > > + slot = id_to_memslot(slots, new->id); > > + if (slot) { > > + old = *slot; > > + } else { > > + WARN_ON_ONCE(change != KVM_MR_CREATE); > > + memset(&old, 0, sizeof(old)); > > + old.id = new->id; > > + old.as_id = as_id; > > + } > > + > > + /* Copy the arch-specific data, again after (re)acquiring slots_arch_lock. */ > > + memcpy(&new->arch, &old.arch, sizeof(old.arch)); > > + > > Is new->arch not initialized before this function is called? Does this > need to be here, or could it be moved above into the first branch of > the if statement? > Oh I see you removed the memset below and replaced it with this. I > think this is fine, but it might be easier to reason about if we left > the memset and moved the memcopy into the if. > No point in doing a memcpy of zeros here. Hmm, good point. I wrote it like this so that the "arch" part is more identifiable since that's what needs to be protected by the lock, but I completely agree that it's odd when viewed without that lens.