Re: [PATCH v3 08/12] KVM: Propagate vcpu explicitly to mark_page_dirty_in_slot()
From: Sean Christopherson <seanjc@google.com>
Date: 2021-11-18 18:53:25
Also in:
kvm, kvm-riscv, kvmarm, linux-arm-kernel, linux-mips, linux-s390
On Thu, Nov 18, 2021, Sean Christopherson wrote:
On Thu, Nov 18, 2021, David Woodhouse wrote:quoted
That leaves the one in TDP MMU handle_changed_spte_dirty_log() which AFAICT can trigger the same crash seen by butt3rflyh4ck — can't that happen from a thread where kvm_get_running_vcpu() is NULL too? For that one I'm not sure.I think could be trigger in the TDP MMU via kvm_mmu_notifier_release() -> kvm_mmu_zap_all(), e.g. if the userspace VMM exits while dirty logging is enabled. That should be easy to (dis)prove via a selftest.
Scratch that, the dirty log update is guarded by the new_spte being present, so
zapping of any kind won't trigger it.
Currently, I believe the only path that would create a present SPTE without an
active vCPU is mmu_notifer.change_pte, but that squeaks by because its required
to be wrapped with invalidate_range_{start,end}(MMU_NOTIFY_CLEAR), and KVM zaps
in that situation.
Ben's series to promote pages on disabling of dirty logging will also sqeuak by
because dirty logging is obviously disabled.