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charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Received-SPF: pass client-ip=170.10.129.124; envelope-from=pbonzini@redhat.com; helo=us-smtp-delivery-124.mimecast.com X-Spam_score_int: -21 X-Spam_score: -2.2 X-Spam_bar: -- X-Spam_report: (-2.2 / 5.0 requ) BAYES_00=-1.9, DKIMWL_WL_HIGH=-0.128, DKIM_SIGNED=0.1, DKIM_VALID=-0.1, DKIM_VALID_AU=-0.1, DKIM_VALID_EF=-0.1, RCVD_IN_DNSWL_NONE=-0.0001, RCVD_IN_MSPIKE_H5=0.001, RCVD_IN_MSPIKE_WL=0.001, RCVD_IN_VALIDITY_CERTIFIED_BLOCKED=0.001, RCVD_IN_VALIDITY_RPBL_BLOCKED=0.001, SPF_HELO_NONE=0.001, SPF_PASS=-0.001 autolearn=ham autolearn_force=no X-Spam_action: no action X-BeenThere: qemu-devel@nongnu.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org Sender: qemu-devel-bounces+qemu-devel=archiver.kernel.org@nongnu.org On 6/3/25 13:47, Xiaoyao Li wrote: > On 6/3/2025 3:41 PM, Xiaoyao Li wrote: >> On 3/29/2025 4:30 AM, Tom Lendacky wrote: >>> A page state change is typically followed by an access of the page(s) >>> and >>> results in another VMEXIT in order to map the page into the nested page >>> table. Depending on the size of page state change request, this can >>> generate a number of additional VMEXITs. For example, under SNP, when >>> Linux is utilizing lazy memory acceptance, memory is typically >>> accepted in >>> 4M chunks. A page state change request is submitted to mark the pages as >>> private, followed by validation of the memory. Since the guest_memfd >>> currently only supports 4K pages, each page validation will result in >>> VMEXIT to map the page, resulting in 1024 additional exits. >>> >>> When performing a page state change, invoke KVM_PRE_FAULT_MEMORY for the >>> size of the page state change in order to pre-map the pages and avoid >>> the >>> additional VMEXITs. This helps speed up boot times. >> >> Unfortunately, it breaks TDX guest. >> >>    kvm_hc_map_gpa_range gpa 0x80000000 size 0x200000 attributes 0x0 >> flags 0x1 >> >> For TDX guest, it uses MAPGPA to maps the range [0x8000 0000, >> +0x0x200000] to shared. The call of KVM_PRE_FAULT_MEMORY on such range >> leads to the TD being marked as bugged >> >> [353467.266761] WARNING: CPU: 109 PID: 295970 at arch/x86/kvm/mmu/ >> tdp_mmu.c:674 tdp_mmu_map_handle_target_level+0x301/0x460 [kvm] > > It turns out to be a KVM bug. > > The gpa passed in in KVM_PRE_FAULT_MEMORY, i.e., range->gpa has no > indication for share vs. private. KVM directly passes range->gpa to > kvm_tdp_map_page() in kvm_arch_vcpu_pre_fault_memory(), which is then > assigned to fault.addr > > However, fault.addr is supposed to be a gpa of real access in TDX guest, > which means it needs to have shared bit set if the map is for shared > access, for TDX case. tdp_mmu_get_root_for_fault() will use it to > determine which root to be used. > > For this case, the pre fault is on the shared memory, while the > fault.addr leads to mirror_root which is for private memory. Thus it > triggers KVM_BUG_ON(). So this would fix it? diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c index 7b3f1783ab3c..66f96476fade 100644 --- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -4895,6 +4895,7 @@ long kvm_arch_vcpu_pre_fault_memory(struct kvm_vcpu *vcpu, { u64 error_code = PFERR_GUEST_FINAL_MASK; u8 level = PG_LEVEL_4K; + u64 direct_bits; u64 end; int r; @@ -4909,15 +4910,18 @@ long kvm_arch_vcpu_pre_fault_memory(struct kvm_vcpu *vcpu, if (r) return r; + direct_bits = 0; if (kvm_arch_has_private_mem(vcpu->kvm) && kvm_mem_is_private(vcpu->kvm, gpa_to_gfn(range->gpa))) error_code |= PFERR_PRIVATE_ACCESS; + else + direct_bits = kvm_gfn_direct_bits(vcpu->kvm); /* * Shadow paging uses GVA for kvm page fault, so restrict to * two-dimensional paging. */ - r = kvm_tdp_map_page(vcpu, range->gpa, error_code, &level); + r = kvm_tdp_map_page(vcpu, range->gpa | direct_bits, error_code, &level); if (r < 0) return r; I'm applying Tom's patch to get it out of his queue, but will delay sending a pull request until the Linux-side fix is accepted. Paolo