Re: [PATCH v3 14/25] KVM: TDX: Bug the VM if extended the initial measurement fails
From: Sean Christopherson <seanjc@google.com>
Date: 2025-10-23 17:27:17
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kvm, kvm-riscv, kvmarm, linux-arm-kernel, linux-coco, linux-mips, linux-riscv, lkml, loongarch
On Tue, Oct 21, 2025, Rick P Edgecombe wrote:
On Thu, 2025-10-16 at 17:32 -0700, Sean Christopherson wrote:quoted
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") Signed-off-by: Yan Zhao <redacted> Signed-off-by: Sean Christopherson <seanjc@google.com> ---Per the discussion in v2, shouldn't it go after patch 24 'KVM: TDX: Guard VM state transitions with "all" the locks'? Otherwise it introduces a KVM_BUG_ON() that can be triggered from userspace. not a huge deal though.
Oh, right. And then the changelog needs to be updated too.