From: Sean Christopherson Date: Thu, 30 Oct 2025 20:09:43 +0000 (-0700) Subject: KVM: TDX: Assert that mmu_lock is held for write when removing S-EPT entries X-Git-Tag: v6.19-rc1~103^2~6^2~13 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=2ff14116982c663066f3cdb4e2af5dfa7a812caa;p=thirdparty%2Fkernel%2Flinux.git KVM: TDX: Assert that mmu_lock is held for write when removing S-EPT entries Unconditionally assert that mmu_lock is held for write when removing S-EPT entries, not just when removing S-EPT entries triggers certain conditions, e.g. needs to do TDH_MEM_TRACK or kick vCPUs out of the guest. Conditionally asserting implies that it's safe to hold mmu_lock for read when those paths aren't hit, which is simply not true, as KVM doesn't support removing S-EPT entries under read-lock. Only two paths lead to remove_external_spte(), and both paths asserts that mmu_lock is held for write (tdp_mmu_set_spte() via lockdep, and handle_removed_pt() via KVM_BUG_ON()). Deliberately leave lockdep assertions in the "no vCPUs" helpers to document that wait_for_sept_zap is guarded by holding mmu_lock for write, and keep the conditional assert in tdx_track() as well, but with a comment to help explain why holding mmu_lock for write matters (above and beyond why tdx_sept_remove_private_spte()'s requirements). Reviewed-by: Binbin Wu Reviewed-by: Kai Huang Reviewed-by: Yan Zhao Tested-by: Yan Zhao Tested-by: Kai Huang Link: https://patch.msgid.link/20251030200951.3402865-21-seanjc@google.com Signed-off-by: Sean Christopherson --- diff --git a/arch/x86/kvm/vmx/tdx.c b/arch/x86/kvm/vmx/tdx.c index a9d1aabbefbf1..ee17c8aacfa44 100644 --- a/arch/x86/kvm/vmx/tdx.c +++ b/arch/x86/kvm/vmx/tdx.c @@ -1715,6 +1715,11 @@ static void tdx_track(struct kvm *kvm) if (unlikely(kvm_tdx->state != TD_STATE_RUNNABLE)) return; + /* + * The full sequence of TDH.MEM.TRACK and forcing vCPUs out of guest + * mode must be serialized, as TDH.MEM.TRACK will fail if the previous + * tracking epoch hasn't completed. + */ lockdep_assert_held_write(&kvm->mmu_lock); err = tdh_mem_track(&kvm_tdx->td); @@ -1762,6 +1767,8 @@ static void tdx_sept_remove_private_spte(struct kvm *kvm, gfn_t gfn, gpa_t gpa = gfn_to_gpa(gfn); u64 err, entry, level_state; + lockdep_assert_held_write(&kvm->mmu_lock); + /* * HKID is released after all private pages have been removed, and set * before any might be populated. Warn if zapping is attempted when