On Tue, Jun 30, 2020 at 08:47:26AM -0700, Sean Christopherson wrote: > On Sat, Jun 27, 2020 at 04:24:34PM +0200, Paolo Bonzini wrote: > > On 26/06/20 20:18, Sean Christopherson wrote: > > >> Btw, would it be more staightforward to check "vcpu->arch.arch_capabilities & > > >> ARCH_CAP_TSX_CTRL_MSR" rather than "*ebx | (F(RTM) | F(HLE))" even if we want > > >> to have such a fix? > > > Not really, That ends up duplicating the check in vmx_get_msr(). From an > > > emulation perspective, this really is a "guest" access to the MSR, in the > > > sense that it the virtual CPU is in the guest domain, i.e. not a god-like > > > entity that gets to break the rules of emulation. > > > > But if you wrote a guest that wants to read MSR_IA32_TSX_CTRL, there are > > two choices: > > > > 1) check ARCH_CAPABILITIES first > > > > 2) blindly access it and default to 0. > > > > Both are fine, because we know MSR_IA32_TSX_CTRL has no > > reserved/must-be-one bits. Calling __kvm_get_msr and checking for an > > invalid MSR through the return value is not breaking the rules of > > emulation, it is "faking" a #GP handler. > > "guest" was the wrong choice of word. My point was that, IMO, emulation > should never set host_initiated=true. > > To me, accessing MSRs with host_initiated is the equivalent of loading a > ucode patch, i.e. it's super duper special stuff that deliberately turns > off all safeguards and can change the fundamental behavior of the (virtual) > CPU. This seems to be an orthogonal change against what this series tried to do. We use host_initiated=true in current code, and this series won't change that fact either. As I mentioned in the other thread, at least the rdmsr warning is ambiguous when it's not initiated from the guest if without this patchset, and this series could address that. > > > So I think Peter's patch is fine, but (possibly on top as a third patch) > > __must_check should be added to MSR getters and setters. Also one > > possibility is to return -EINVAL for invalid MSRs. Yeah I can add another patch for that. Also if to repost, I tend to also introduce KVM_MSR_RET_[OK|ERROR] too, which seems to be cleaner when we had KVM_MSR_RET_INVALID. Any objections before I repost? -- Peter Xu
