On 24/10/2017 15:49, Ren Kimura wrote: > Hi. > I'm using KVM guest page tracking API like, > kvm_page_track_register_notifier/kvm_page_track_add_page for my > project. > https://lwn.net/Articles/675571/ > > But I can't catch some points about these API. So would anyone help me? > > My primary question is how track_write is called? > track_write hook function seems to be called by kvm_page_track_write > from emulator_write_phys. > > https://github.com/torvalds/linux/blob/3206e7d5e25ef94b5a29e2c81e6fb8d5fb48422f/arch/x86/kvm/x86.c#L4601 > > But page hook is set by removing write permission from spte. (assuming > direct shadow paging case) > When EPT violation happen due to writing this page, how is > emulator_write_phys called? When kvm_mmu_page_fault calls vcpu->arch.mmu.page_fault, the implementation of the function (tdp_page_fault for EPT) calls page_fault_handle_page_track. If page_fault_handle_page_track says that the page is being tracked, tdp_page_fault returns 1 which causes emulation to run. (As an aside, the magic "1" will change to RET_PF_EMULATE in 4.15, which is more self-explanatory). Paolo
