On 09/11/2017 11:47, Wanpeng Li wrote: > 2017-11-09 18:40 GMT+08:00 Paolo Bonzini <pbonzini@xxxxxxxxxx>: >> On 09/11/2017 01:37, Wanpeng Li wrote: >>> 2017-11-09 5:47 GMT+08:00 Jim Mattson <jmattson@xxxxxxxxxx>: >>>> I realize now that there are actually many other problems with >>>> deferring some control field checks to the hardware VM-entry of >>>> vmcs02. When there is an invalid control field, the vCPU should just >>>> fall through to the next instruction, without any state modifiation >>>> other than the ALU flags and the VM-instruction error field of the >>>> current VMCS. However, in preparation for the hardware VM-entry of >>>> vmcs02, we have already changed quite a bit of the vCPU state: the >>>> MSRs on the VM-entry MSR-load list, DR7, IA32_DEBUGCTL, the entire >>>> FLAGS register, etc. All of these changes should be undone, and we're >>>> not prepared to do that. (For instance, what was the old DR7 value >>>> that needs to be restored?) >>> I didn't observe real issue currently, and I hope this patchset can >>> catch the upcoming merge window. Then we can dig more into your >>> concern. >> >> Can any of you write a simple testcase for just one bug (e.g. DR7)? > > Jim you can have a try for your concern, I have already tried tons of > stress testing and didn't observe any issue. You need to craft a testcase for kvm-unit-tests. No stress testing will find an issue. Your patch is fine, but Jim is saying that we cannot really skip the check for invalid control fields. It's a more general issue that can be fixed by adding explicit checks in KVM. Paolo
