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[34.105.13.176]) by smtp.gmail.com with ESMTPSA id d9443c01a7336-22ac7ccb79esm121945215ad.243.2025.04.15.13.06.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 15 Apr 2025 13:06:40 -0700 (PDT) Date: Tue, 15 Apr 2025 13:06:35 -0700 From: Vipin Sharma To: Sean Christopherson Cc: Paolo Bonzini , kvm@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH v2 3/3] KVM: x86/mmu: Defer allocation of shadow MMU's hashed page list Message-ID: <20250415200635.GA210309.vipinsh@google.com> References: <20250401155714.838398-1-seanjc@google.com> <20250401155714.838398-4-seanjc@google.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20250401155714.838398-4-seanjc@google.com> On 2025-04-01 08:57:14, Sean Christopherson wrote: > +static __ro_after_init HLIST_HEAD(empty_page_hash); > + > +static struct hlist_head *kvm_get_mmu_page_hash(struct kvm *kvm, gfn_t gfn) > +{ > + struct hlist_head *page_hash = READ_ONCE(kvm->arch.mmu_page_hash); > + > + if (!page_hash) > + return &empty_page_hash; > + > + return &page_hash[kvm_page_table_hashfn(gfn)]; > +} > + > > @@ -2357,6 +2368,7 @@ static struct kvm_mmu_page *__kvm_mmu_get_shadow_page(struct kvm *kvm, > struct kvm_mmu_page *sp; > bool created = false; > > + BUG_ON(!kvm->arch.mmu_page_hash); > sp_list = &kvm->arch.mmu_page_hash[kvm_page_table_hashfn(gfn)]; Why do we need READ_ONCE() at kvm_get_mmu_page_hash() but not here? My understanding is that it is in kvm_get_mmu_page_hash() to avoid compiler doing any read tear. If yes, then the same condition is valid here, isn't it?