On 03/08/21 17:11, Sean Christopherson wrote:
On top of this, I think the CD case (kvm_post_set_cr0) can be changed to use
kvm_mmu_zap_all_fast.
No, because fast zap requires kvm->slots_lock be held.
Yeah, that much I knew. :) The issue is the usual ordering between
slots_lock and SRCU.
Paolo
That could be relaxed by
reverting ca333add6933 ("KVM: x86/mmu: Explicitly track only a single invalid mmu
generation") and converting mmu_valid_gen to a u64 (to prevent wrap on 32-bit KVM).
IMO the extra memory cost, even though it's meager savings when using TDP without
nested, isn't worth relaxing the rules for fast zap. Non-coherent DMA isn't very
common these days, and toggling CR0.CD is a rare guest operation (it'd probably
never happen if the darn architcture didn't set it on RESET).
