On Thu, Jan 05, 2023 at 11:23:01AM +0000, Jarkko Sakkinen wrote: > On Fri, Dec 02, 2022 at 02:13:41PM +0800, Chao Peng wrote: > > In memory encryption usage, guest memory may be encrypted with special > > key and can be accessed only by the guest itself. We call such memory > > private memory. It's valueless and sometimes can cause problem to allow > > userspace to access guest private memory. This new KVM memslot extension > > allows guest private memory being provided through a restrictedmem > > backed file descriptor(fd) and userspace is restricted to access the > > bookmarked memory in the fd. > > > > This new extension, indicated by the new flag KVM_MEM_PRIVATE, adds two > > additional KVM memslot fields restricted_fd/restricted_offset to allow > > userspace to instruct KVM to provide guest memory through restricted_fd. > > 'guest_phys_addr' is mapped at the restricted_offset of restricted_fd > > and the size is 'memory_size'. > > > > The extended memslot can still have the userspace_addr(hva). When use, a > > single memslot can maintain both private memory through restricted_fd > > and shared memory through userspace_addr. Whether the private or shared > > part is visible to guest is maintained by other KVM code. > > > > A restrictedmem_notifier field is also added to the memslot structure to > > allow the restricted_fd's backing store to notify KVM the memory change, > > KVM then can invalidate its page table entries or handle memory errors. > > > > Together with the change, a new config HAVE_KVM_RESTRICTED_MEM is added > > and right now it is selected on X86_64 only. > > > > To make future maintenance easy, internally use a binary compatible > > alias struct kvm_user_mem_region to handle both the normal and the > > '_ext' variants. > > Feels bit hacky IMHO, and more like a completely new feature than > an extension. > > Why not just add a new ioctl? The commit message does not address > the most essential design here. Yes, people can always choose to add a new ioctl for this kind of change and the balance point here is we want to also avoid 'too many ioctls' if the functionalities are similar. The '_ext' variant reuses all the existing fields in the 'normal' variant and most importantly KVM internally can reuse most of the code. I certainly can add some words in the commit message to explain this design choice. Thanks, Chao > > BR, Jarkko
