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Tue, 24 Dec 2024 06:31:22 -0800 (PST) X-Google-Smtp-Source: AGHT+IFUvdABnkVt+9LSKjCliq/5aNwgQOJO2/oDO5XrjmE0f2woMAZpAYXB5RSfz5sTBfurXrcoYQ== X-Received: by 2002:a05:6000:4a0d:b0:385:dedb:a156 with SMTP id ffacd0b85a97d-38a221ed2e7mr13008881f8f.6.1735050681589; Tue, 24 Dec 2024 06:31:21 -0800 (PST) Received: from [192.168.10.27] ([151.81.118.45]) by smtp.googlemail.com with ESMTPSA id 5b1f17b1804b1-4366a093cbfsm142487575e9.22.2024.12.24.06.31.20 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 24 Dec 2024 06:31:20 -0800 (PST) Message-ID: Date: Tue, 24 Dec 2024 15:31:19 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v2 22/24] KVM: TDX: Finalize VM initialization To: Yan Zhao , seanjc@google.com, kvm@vger.kernel.org, dave.hansen@linux.intel.com Cc: rick.p.edgecombe@intel.com, kai.huang@intel.com, adrian.hunter@intel.com, reinette.chatre@intel.com, xiaoyao.li@intel.com, tony.lindgren@intel.com, binbin.wu@linux.intel.com, dmatlack@google.com, isaku.yamahata@intel.com, isaku.yamahata@gmail.com, nik.borisov@suse.com, linux-kernel@vger.kernel.org, x86@kernel.org References: <20241112073327.21979-1-yan.y.zhao@intel.com> <20241112073848.22298-1-yan.y.zhao@intel.com> From: Paolo Bonzini Content-Language: en-US Autocrypt: addr=pbonzini@redhat.com; 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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit On 11/12/24 08:38, Yan Zhao wrote: > From: Isaku Yamahata > > Introduce a new VM-scoped KVM_MEMORY_ENCRYPT_OP IOCTL subcommand, > KVM_TDX_FINALIZE_VM, to perform TD Measurement Finalization. > > The API documentation is provided in a separate patch: > “Documentation/virt/kvm: Document on Trust Domain Extensions (TDX)”. > > Enhance TDX’s set_external_spte() hook to record the pre-mapping count > instead of returning without action when the TD is not finalized. > > Adjust the pre-mapping count when pages are added or if the mapping is > dropped. > > Set pre_fault_allowed to true after the finalization is complete. > > Note: TD Measurement Finalization is the process by which the initial state > of the TDX VM is measured for attestation purposes. It uses the SEAMCALL > TDH.MR.FINALIZE, after which: > 1. The VMM can no longer add TD private pages with arbitrary content. > 2. The TDX VM becomes runnable. > > Signed-off-by: Isaku Yamahata > Co-developed-by: Adrian Hunter > Signed-off-by: Adrian Hunter > Co-developed-by: Rick Edgecombe > Signed-off-by: Rick Edgecombe > Signed-off-by: Yan Zhao > --- > TDX MMU part 2 v2 > - Merge changes from patch "KVM: TDX: Premap initial guest memory" into > this patch (Paolo) > - Consolidate nr_premapped counting into this patch (Paolo) > - Page level check should be (and is) in tdx_sept_set_private_spte() in > patch "KVM: TDX: Implement hooks to propagate changes of TDP MMU mirror > page table" not in tdx_mem_page_record_premap_cnt() (Paolo) > - Protect finalization using kvm->slots_lock (Paolo) > - Set kvm->arch.pre_fault_allowed to true after finalization is done > (Paolo) > - Add a memory barrier to ensure correct ordering of the updates to > kvm_tdx->finalized and kvm->arch.pre_fault_allowed (Adrian) > - pre_fault_allowed must not be true before finalization is done. > Highlight that fact by checking it in tdx_mem_page_record_premap_cnt() > (Adrian) > - No need for is_td_finalized() (Rick) > - Fixup SEAMCALL call sites due to function parameter changes to SEAMCALL > wrappers (Kai) > - Add nr_premapped where it's first used (Tao) I have just a couple imprecesions to note: - stale reference to 'finalized' - atomic64_read WARN should block the following atomic64_dec (there is still a small race window but it's not worth using a dec-if-not-zero operation) - rename tdx_td_finalizemr to tdx_td_finalize diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c index 61e4f126addd..eb0de85c3413 100644 --- a/arch/x86/kvm/vmx/tdx.c +++ b/arch/x86/kvm/vmx/tdx.c @@ -609,8 +609,8 @@ int tdx_sept_set_private_spte(struct kvm *kvm, gfn_t gfn, get_page(pfn_to_page(pfn)); /* - * To match ordering of 'finalized' and 'pre_fault_allowed' in - * tdx_td_finalizemr(). + * Read 'pre_fault_allowed' before 'kvm_tdx->state'; see matching + * barrier in tdx_td_finalize(). */ smp_rmb(); if (likely(kvm_tdx->state == TD_STATE_RUNNABLE)) @@ -1397,7 +1397,7 @@ void tdx_flush_tlb_all(struct kvm_vcpu *vcpu) ept_sync_global(); } -static int tdx_td_finalizemr(struct kvm *kvm, struct kvm_tdx_cmd *cmd) +static int tdx_td_finalize(struct kvm *kvm, struct kvm_tdx_cmd *cmd) { struct kvm_tdx *kvm_tdx = to_kvm_tdx(kvm); @@ -1452,7 +1452,7 @@ int tdx_vm_ioctl(struct kvm *kvm, void __user *argp) r = tdx_td_init(kvm, &tdx_cmd); break; case KVM_TDX_FINALIZE_VM: - r = tdx_td_finalizemr(kvm, &tdx_cmd); + r = tdx_td_finalize(kvm, &tdx_cmd); break; default: r = -EINVAL; @@ -1715,8 +1715,8 @@ static int tdx_gmem_post_populate(struct kvm *kvm, gfn_t gfn, kvm_pfn_t pfn, goto out; } - WARN_ON_ONCE(!atomic64_read(&kvm_tdx->nr_premapped)); - atomic64_dec(&kvm_tdx->nr_premapped); + if (!WARN_ON_ONCE(!atomic64_read(&kvm_tdx->nr_premapped))) + atomic64_dec(&kvm_tdx->nr_premapped); if (arg->flags & KVM_TDX_MEASURE_MEMORY_REGION) { for (i = 0; i < PAGE_SIZE; i += TDX_EXTENDMR_CHUNKSIZE) {