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Fri, 15 Sep 2023 07:26:18 -0700 (PDT) Date: Fri, 15 Sep 2023 07:26:16 -0700 In-Reply-To: Mime-Version: 1.0 References: <20230914015531.1419405-1-seanjc@google.com> <20230914015531.1419405-19-seanjc@google.com> Message-ID: Subject: Re: [RFC PATCH v12 18/33] KVM: x86/mmu: Handle page fault for private memory From: Sean Christopherson To: Yan Zhao Cc: Paolo Bonzini , Marc Zyngier , Oliver Upton , Huacai Chen , Michael Ellerman , Anup Patel , Paul Walmsley , Palmer Dabbelt , Albert Ou , "Matthew Wilcox (Oracle)" , Andrew Morton , Paul Moore , James Morris , "Serge E. Hallyn" , kvm@vger.kernel.org, linux-arm-kernel@lists.infradead.org, kvmarm@lists.linux.dev, linux-mips@vger.kernel.org, linuxppc-dev@lists.ozlabs.org, kvm-riscv@lists.infradead.org, linux-riscv@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-mm@kvack.org, linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org, Chao Peng , Fuad Tabba , Jarkko Sakkinen , Anish Moorthy , Yu Zhang , Isaku Yamahata , Xu Yilun , Vlastimil Babka , Vishal Annapurve , Ackerley Tng , Maciej Szmigiero , David Hildenbrand , Quentin Perret , Michael Roth , Wang , Liam Merwick , Isaku Yamahata , "Kirill A . Shutemov" Content-Type: text/plain; charset="us-ascii" X-Rspamd-Queue-Id: A071080023 X-Rspam-User: X-Stat-Signature: 1wx5iz7gringmkw1ijrr1jkos8a6h5on X-Rspamd-Server: rspam03 X-HE-Tag: 1694787979-279471 X-HE-Meta: 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 iqVKhTtA 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Fri, Sep 15, 2023, Yan Zhao wrote: > On Wed, Sep 13, 2023 at 06:55:16PM -0700, Sean Christopherson wrote: > .... > > +static void kvm_mmu_prepare_memory_fault_exit(struct kvm_vcpu *vcpu, > > + struct kvm_page_fault *fault) > > +{ > > + kvm_prepare_memory_fault_exit(vcpu, fault->gfn << PAGE_SHIFT, > > + PAGE_SIZE, fault->write, fault->exec, > > + fault->is_private); > > +} > > + > > +static int kvm_faultin_pfn_private(struct kvm_vcpu *vcpu, > > + struct kvm_page_fault *fault) > > +{ > > + int max_order, r; > > + > > + if (!kvm_slot_can_be_private(fault->slot)) { > > + kvm_mmu_prepare_memory_fault_exit(vcpu, fault); > > + return -EFAULT; > > + } > > + > > + r = kvm_gmem_get_pfn(vcpu->kvm, fault->slot, fault->gfn, &fault->pfn, > > + &max_order); > > + if (r) { > > + kvm_mmu_prepare_memory_fault_exit(vcpu, fault); > > + return r; > > + } > > + > > + fault->max_level = min(kvm_max_level_for_order(max_order), > > + fault->max_level); > > + fault->map_writable = !(fault->slot->flags & KVM_MEM_READONLY); > > + > > + return RET_PF_CONTINUE; > > +} > > + > > static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault) > > { > > struct kvm_memory_slot *slot = fault->slot; > > @@ -4293,6 +4356,14 @@ static int __kvm_faultin_pfn(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault > > return RET_PF_EMULATE; > > } > > > > + if (fault->is_private != kvm_mem_is_private(vcpu->kvm, fault->gfn)) { > In patch 21, > fault->is_private is set as: > ".is_private = kvm_mem_is_private(vcpu->kvm, cr2_or_gpa >> PAGE_SHIFT)", > then, the inequality here means memory attribute has been updated after > last check. > So, why an exit to user space for converting is required instead of a mere retry? > > Or, is it because how .is_private is assigned in patch 21 is subjected to change > in future? This. Retrying on SNP or TDX would hang the guest. I suppose we could special case VMs where .is_private is derived from the memory attributes, but the SW_PROTECTED_VM type is primary a development vehicle at this point. I'd like to have it mimic SNP/TDX as much as possible; performance is a secondary concern. E.g. userspace needs to be prepared for "spurious" exits due to races on SNP and TDX, which this can theoretically exercise. Though the window is quite small so I doubt that'll actually happen in practice; which of course also makes it less important to retry instead of exiting.