On Sat, Sep 14, 2024 at 05:27:32PM +0800, Yan Zhao wrote: > > Similarly, can tdh_mem_page_aug() actually contend with tdg_mem_page_accept()? > > The page isn't yet mapped, so why would the guest be allowed to take a lock on > > the S-EPT entry? > Before tdg_mem_page_accept() accepts a gpa and set rwx bits in a SPTE, if second > tdh_mem_page_aug() is called on the same gpa, the second one may contend with > tdg_mem_page_accept(). > > But given KVM does not allow the second tdh_mem_page_aug(), looks the contention > between tdh_mem_page_aug() and tdg_mem_page_accept() will not happen. I withdraw the reply above. tdh_mem_page_aug() and tdg_mem_page_accept() both attempt to modify the same SEPT entry, leading to contention. - tdg_mem_page_accept() first walks the SEPT tree with no lock to get the SEPT entry. 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.
