Il 13/08/2013 16:33, Florian Pester ha scritto: > Hi, > > for a uni project I'm trying to write a userspace for KVM that can run > ELF binaries without a full blown OS in the guest. The idea is to handle > any syscalls made by the binary running inside the guest in the > userspace of the host. In the simplest case you could forward them to > the host Linux kernel. > > In any case, I've gotten pretty far, setting up IDTs, the VCPU, Page > Tables and whatnot, but right now I'm stuck. I setup my syscall handler > to do a VMCALL, which according to the Intel manual is supposed to > return control to the host. However this seems to be handled by KVM > without an exit into userspace? Yes, this is correct. > If this is correct, is there any way to make a call to the host VMM, > that will be transfered to userspace by KVM? You could patch kvm_emulate_hypercall to return to userspace on an unknown VMCALL. The simplest implementation could be something like vcpu->run->exit_reason = KVM_EXIT_HYPERCALL; return 0; in vmx.c's handle_vmcall and similarly for svm.c's vmmcall_interception. If you want to make a patch for upstream, it is a bit more complicated because of backwards-compatibility. You will need a new capability and you will need to enable it with KVM_ENABLE_CAP, which right now is only used by PowerPC KVM. However, this "hypercall to userspace" functionality used to be there and was removed, so it is unlikely to resurrect... I suggest you use simply an "out" to an otherwise unused port. Paolo -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
