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AJvYcCVvuo77wZvH4xkk1ozniYJz6WBwO8hUM7TSpLMAxxr6nKnL53AxVtu9ZW2DnTyAl8S9v96f677HuPS7@lists.linux.dev X-Gm-Message-State: AOJu0YxdHSQWuRrhKpURCHlATEwURTGWchKXulGmRMcuT2FYo80NHlST dCr5tzaT0VXEtDbAWg/aqpsLkMWqTzU1qhPGhMPTZsF/H/V+Os2fpUY36kJjigako52iS6vbGO7 1dQFfEg== X-Google-Smtp-Source: AGHT+IHEqEX/8GwSPDTtO9R4g/+ZtFO0C94Pe4ULgHF/AbXONvqtNga/vyT3hE3hD5zVd0KE3EnoXL2eWbI= X-Received: from pjyj8.prod.google.com ([2002:a17:90a:e608:b0:33b:51fe:1a8b]) (user=seanjc job=prod-delivery.src-stubby-dispatcher) by 2002:a17:902:db05:b0:24e:3cf2:2450 with SMTP id d9443c01a7336-290c9c8a5e6mr368813165ad.2.1761323744332; Fri, 24 Oct 2025 09:35:44 -0700 (PDT) Date: Fri, 24 Oct 2025 09:35:43 -0700 In-Reply-To: <442f5488e4a66f6a1517082df3d2ae47316be010.camel@intel.com> Precedence: bulk X-Mailing-List: linux-coco@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: Mime-Version: 1.0 References: <20251017003244.186495-1-seanjc@google.com> <20251017003244.186495-15-seanjc@google.com> <442f5488e4a66f6a1517082df3d2ae47316be010.camel@intel.com> Message-ID: Subject: Re: [PATCH v3 14/25] KVM: TDX: Bug the VM if extended the initial measurement fails From: Sean Christopherson To: Kai Huang Cc: "chenhuacai@kernel.org" , "frankja@linux.ibm.com" , "maz@kernel.org" , "borntraeger@linux.ibm.com" , "pjw@kernel.org" , "aou@eecs.berkeley.edu" , "kas@kernel.org" , "maobibo@loongson.cn" , "pbonzini@redhat.com" , "maddy@linux.ibm.com" , "palmer@dabbelt.com" , "imbrenda@linux.ibm.com" , "zhaotianrui@loongson.cn" , "anup@brainfault.org" , "oliver.upton@linux.dev" , "kvm@vger.kernel.org" , "linux-coco@lists.linux.dev" , Yan Y Zhao , "michael.roth@amd.com" , "linux-kernel@vger.kernel.org" , Ira Weiny , "loongarch@lists.linux.dev" , "binbin.wu@linux.intel.com" , "ackerleytng@google.com" , "kvmarm@lists.linux.dev" , "kvm-riscv@lists.infradead.org" , Vishal Annapurve , "linuxppc-dev@lists.ozlabs.org" , Rick P Edgecombe , "linux-mips@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "linux-riscv@lists.infradead.org" , "x86@kernel.org" Content-Type: text/plain; charset="us-ascii" On Thu, Oct 23, 2025, Kai Huang wrote: > On Thu, 2025-10-16 at 17:32 -0700, Sean Christopherson wrote: > > WARN and terminate the VM if TDH_MR_EXTEND fails, as extending the > > measurement should fail if and only if there is a KVM bug, or if the S-EPT > > mapping is invalid, and it should be impossible for the S-EPT mappings to > > be removed between kvm_tdp_mmu_map_private_pfn() and tdh_mr_extend(). > > > > Holding slots_lock prevents zaps due to memslot updates, > > filemap_invalidate_lock() prevents zaps due to guest_memfd PUNCH_HOLE, > > and all usage of kvm_zap_gfn_range() is mutually exclusive with S-EPT > > entries that can be used for the initial image. The call from sev.c is > > obviously mutually exclusive, TDX disallows KVM_X86_QUIRK_IGNORE_GUEST_PAT > > so same goes for kvm_noncoherent_dma_assignment_start_or_stop, and while > > __kvm_set_or_clear_apicv_inhibit() can likely be tripped while building the > > image, the APIC page has its own non-guest_memfd memslot and so can't be > > used for the initial image, which means that too is mutually exclusive. > > > > Opportunistically switch to "goto" to jump around the measurement code, > > partly to make it clear that KVM needs to bail entirely if extending the > > measurement fails, partly in anticipation of reworking how and when > > TDH_MEM_PAGE_ADD is done. > > > > Fixes: d789fa6efac9 ("KVM: TDX: Handle vCPU dissociation") > > So IIUC this patch only adds a KVM_BUG_ON() when TDH.MR.EXTEND fails. How > does this fix anything? Hmm, yeah, I'll drop the Fixes. It made more sense when I thought it was impossible for tdh_mr_extend() to fail, as returning an error and not explicitly terminating the VM was "wrong". But I agree it does far more harm than good, even when relocated to the end of the series.