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Tue, 30 Jul 2024 15:35:20 -0700 (PDT) Date: Tue, 30 Jul 2024 15:35:18 -0700 In-Reply-To: <419ea6ce-83ca-413e-936c-1935e2c51497@redhat.com> Mime-Version: 1.0 References: <20240726235234.228822-1-seanjc@google.com> <419ea6ce-83ca-413e-936c-1935e2c51497@redhat.com> Message-ID: Subject: Re: [PATCH v12 00/84] KVM: Stop grabbing references to PFNMAP'd pages From: Sean Christopherson To: Paolo Bonzini Cc: 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-20240730_153522_141250_C893C0DF X-CRM114-Status: GOOD ( 12.36 ) 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 Tue, Jul 30, 2024, Paolo Bonzini wrote: > An interesting evolution of the API could be to pass a struct kvm_follow_pfn > pointer to {,__}kvm_faultin_pfn() and __gfn_to_page() (the "constructors"); > and on the other side to kvm_release_faultin_page() and > kvm_release_page_*(). The struct kvm_follow_pfn could be embedded in the > (x86) kvm_page_fault and (generic) kvm_host_map structs. But certainly not > as part of this already huge work. For kvm_faultin_pfn(), my hope/dream is to make kvm_page_fault a common struct, with an arch member (a la kvm_vcpu), and get to something like: static int arch_page_fault_handler(...) { struct kvm_page_fault fault = { , .arch.xxx = , }; r = kvm_faultin_pfn(); ... } In theory, that would allow moving the kvm->mmu_invalidate_seq handling, memslot lookup, etc. into kvm_faultin_pfn(), or maybe another helper that is invoked to setup the fault structure. I.e. it would give us a way to drive convergence for at least some of the fault handling logic, without having to tackle gory arch details, at least not right away.