Hi, I'm learning about qemu KVM, looking into code and experimenting on it. I have the following doubts regarding it, I would be grateful if you help me to get some idea on them. 1. I observe that KVM allocates memory to guests when it needs it but doesn't take it back (except for ballooning case). Also, the Qemu/KVM process does not free the memory even when the guest is rebooted. In this case, Does the Guest VM get access to memory already pre-filled with some garbage from the previous run?? (Since the host would allocate zeroed pages to guests the first time it requests but after that it's up to guests). Can it be a security issue? 2. How does the KVM know if GPFN (guest physical frame number) is backed by an actual machine frame number in host? If not mapped, then it faults in the host and allocates a physical frame for guests in the host. (kvm_mmu_page_fault) 3. How/where can I access the GPFNs in the host? Is "gfn_t gfn = gpa >> PAGE_SHIFT" and "gpa_t cr2_or_gpa" in the KVM page fault handler, x86 is the same as GPFN. (that is can I use pfn_to_page in guest VM to access the struct page in Guest) Thank You. Best Regards, Shivank Garg M.Tech Student, IIT Kanpur
