Deprecate BUG() in pte_list_remove() in shadow mmu to avoid crashing a physical machine. There are several reasons and motivations to do so: MMU bug is difficult to discover due to various racing conditions and corner cases and thus it extremely hard to debug. The situation gets much worse when it triggers the shutdown of a host. Host machine crash might eliminates everything including the potential clues for debugging. >From cloud computing service perspective, BUG() or BUG_ON() is probably no longer appropriate as the host reliability is top priority. Crashing the physical machine is almost never a good option as it eliminates innocent VMs and cause service outage in a larger scope. Even worse, if attacker can reliably triggers this code by diverting the control flow or corrupting the memory, then this becomes vm-of-death attack. This is a huge attack vector to cloud providers, as the death of one single host machine is not the end of the story. Without manual interferences, a failed cloud job may be dispatched to other hosts and continue host crashes until all of them are dead. For the above reason, we propose the replacement of BUG() in pte_list_remove() with KVM_BUG() to crash just the VM itself. v3 - v4: - update code to integrate messages into KVM_BUG() [seanjc]. - update commit message [seanjc]. v2 -> v3: - plumb @kvm all the way to pte_list_remove() [seanjc, pbonzini] - https://lore.kernel.org/lkml/20221128002043.1555543-1-mizhang@xxxxxxxxxx/ v1 -> v2: - compile test the code. - fill KVM_BUG() with kvm_get_running_vcpu()->kvm - https://lore.kernel.org/all/20221124003505.424617-1-mizhang@xxxxxxxxxx/ rfc v1: - https://lore.kernel.org/all/20221123231206.274392-1-mizhang@xxxxxxxxxx/ Mingwei Zhang (2): KVM: x86/mmu: plumb struct kvm all the way to pte_list_remove() KVM: x86/mmu: replace BUG() with KVM_BUG() in shadow mmu arch/x86/kvm/mmu/mmu.c | 33 +++++++++++++++++---------------- 1 file changed, 17 insertions(+), 16 deletions(-) -- 2.38.1.584.g0f3c55d4c2-goog
