Il 04/08/2014 10:37, Morty Andersen ha scritto: > Hi > > I'm working on an extension to QEMU (target i386). This involves adding > new MSR's. I've got it working in non-KVM mode by adding these MSR's to > the state and adding extra cases to helper_wrmsr(), helper_rdmsr(). The > guest can now read/write these MSR's as expected. However, it fails when > running in KVM-mode. Specifically, writing the MSR's causes GPF. Note > that these MSR's are not natively supported by the host CPU. I don't > know enough about Intel's VMX to tell if it is even reasonable to expect > that this could work for a non-natively supported MSR. As far as I can > read in the VMX documentation, the hypervisor can setup a bitmap of > which MSR's should cause trap's to the hypervisor and which shouldn't. I > guess it would be the KVM kernel module that does this based on input it > receives from QEMU. But I haven't been able to find the part of QEMU > that negotiates this. I guess the solution for me is to set the > necessary bits to that access to the new MSR's causes traps. Next, I > need to add/modify the trap handler so that it can handle the MSR's.
Hi, handling of the MSRs in KVM is done entirely in the hypervisor. QEMU only gets/sets them in order to support migration. You need to modify the KVM kernel module for the VM to recognize your special MSRs. Paolo
