From: Sean Christopherson Date: Fri, 11 Oct 2024 02:10:40 +0000 (-0700) Subject: KVM: x86/mmu: WARN and flush if resolving a TDP MMU fault clears MMU-writable X-Git-Tag: v6.13-rc1~13^2~16^2~20 X-Git-Url: https://git.kernel.dk/?a=commitdiff_plain;h=1a175082b190190d9d05a0a5927b72cbb657fd1d;p=linux-2.6-block.git KVM: x86/mmu: WARN and flush if resolving a TDP MMU fault clears MMU-writable Do a remote TLB flush if installing a leaf SPTE overwrites an existing leaf SPTE (with the same target pfn, which is enforced by a BUG() in handle_changed_spte()) and clears the MMU-Writable bit. Since the TDP MMU passes ACC_ALL to make_spte(), i.e. always requests a Writable SPTE, the only scenario in which make_spte() should create a !MMU-Writable SPTE is if the gfn is write-tracked or if KVM is prefetching a SPTE. When write-protecting for write-tracking, KVM must hold mmu_lock for write, i.e. can't race with a vCPU faulting in the SPTE. And when prefetching a SPTE, the TDP MMU takes care to avoid clobbering a shadow-present SPTE, i.e. it should be impossible to replace a MMU-writable SPTE with a !MMU-writable SPTE when handling a TDP MMU fault. Cc: David Matlack Cc: Yan Zhao Link: https://lore.kernel.org/r/20241011021051.1557902-9-seanjc@google.com Signed-off-by: Sean Christopherson --- diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c index 9c66be7fb002..bc9e2f50dc80 100644 --- a/arch/x86/kvm/mmu/tdp_mmu.c +++ b/arch/x86/kvm/mmu/tdp_mmu.c @@ -1033,7 +1033,9 @@ static int tdp_mmu_map_handle_target_level(struct kvm_vcpu *vcpu, else if (tdp_mmu_set_spte_atomic(vcpu->kvm, iter, new_spte)) return RET_PF_RETRY; else if (is_shadow_present_pte(iter->old_spte) && - !is_last_spte(iter->old_spte, iter->level)) + (!is_last_spte(iter->old_spte, iter->level) || + WARN_ON_ONCE(is_mmu_writable_spte(iter->old_spte) && + !is_mmu_writable_spte(new_spte)))) kvm_flush_remote_tlbs_gfn(vcpu->kvm, iter->gfn, iter->level); /*