2017-08-03 09:05-0700, Jim Mattson: > On Thu, Aug 3, 2017 at 8:36 AM, Radim Krčmář <rkrcmar@xxxxxxxxxx> wrote: > > 2017-08-03 16:09+0200, David Hildenbrand: > >> /* > >> * If translation failed, no matter: This feature asks > >> * to exit when accessing the given address, and if it > >> * can never be accessed, this feature won't do > >> * anything anyway. > >> */ > > This comment is incorrect. On real hardware, the APIC access page > doesn't have to exist (i.e. be backed by actual memory), because the > APIC access page is never accessed. Think of the APIC access page as a > sentinel value that the hypervisor can put in the page tables (EPT > page tables if they are in use, x86 page tables otherwise) to trigger > APIC virtualization. If there is an access, it is to the page at the > virtual APIC address, not the APIC access page. Right, > Similarly, in a VM, there need not be a mapping for the APIC access > page for the feature to work as architected. (Or, at least, that's the > way it should work. :-) the APIC_ACCESS_ADDR is always L0 physical address, so we somehow need to map the L1 physical address somewhere in order to recognize accesses from L2. I think the correct way would be to should create a new mapping if the chosen L1 physical address has no L0 physical address yet. The code was made for the common case where hypervisors select a page that is mapped by KVM ... Do you wish to send patches? :) Thanks.
