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It then acquire the guest side lock of the found SEPT entry before > checking entry state. > - tdh_mem_page_aug() first walks the SEPT tree with shared lock to locate the > SEPT entry to modify, it then aquires host side lock of the SEPT entry before > checking entry state. This seems can only happen when there are multiple threads in guest trying to do tdg_mem_page_accept() on the same page. This should be extremely rare to happen, and if this happens, it will eventually result in another fault in KVM. So now we set SPTE to FROZEN_SPTE before doing AUG to prevent from other threads from going on. I think when tdh_mem_page_aug() fails with secure EPT "entry" busy, we can reset FROZEN_SPTE back to old_spte and return PF_RETRY so that this thread and another fault thread can both try to complete AUG again? The thread fails with AUG can also go back to guest though, but since host priority bit is already set, the further PAGE.ACCEPT will fail but this is fine due to another AUG in KVM will eventually resolve this and make progress to the guest.