On Tue, Nov 01, 2022, Vitaly Kuznetsov wrote: > Sean Christopherson <seanjc@xxxxxxxxxx> writes: > > > On Tue, Nov 01, 2022, Vitaly Kuznetsov wrote: > >> Hyper-V MSR-Bitmap tests do RDMSR from L2 to exit to L1. While 'evmcs_test' > >> correctly clobbers all GPRs (which are not preserved), 'hyperv_svm_test' > >> does not. Introduce and use common rdmsr_from_l2() to avoid code > >> duplication and remove hardcoding of MSRs. > >> > >> Signed-off-by: Vitaly Kuznetsov <vkuznets@xxxxxxxxxx> > >> --- > >> .../selftests/kvm/include/x86_64/processor.h | 9 +++++++ > >> .../testing/selftests/kvm/x86_64/evmcs_test.c | 24 ++++--------------- > >> .../selftests/kvm/x86_64/hyperv_svm_test.c | 8 +++---- > >> 3 files changed, 17 insertions(+), 24 deletions(-) > >> > >> diff --git a/tools/testing/selftests/kvm/include/x86_64/processor.h b/tools/testing/selftests/kvm/include/x86_64/processor.h > >> index fbaf0b6cec4b..a14b7e4ea7c4 100644 > >> --- a/tools/testing/selftests/kvm/include/x86_64/processor.h > >> +++ b/tools/testing/selftests/kvm/include/x86_64/processor.h > >> @@ -520,6 +520,15 @@ static inline void cpu_relax(void) > >> "hlt\n" \ > >> ) > >> > >> +/* Exit to L1 from L2 with RDMSR instruction */ > >> +static inline void rdmsr_from_l2(uint32_t msr) > > > > I would prefer keeping this helper out of common x86-64 code, even if it means > > duplicating code across multiple Hyper-V tests until the L1 VM-Enter/VM-Exit > > sequences get cleaned up. The name is misleading, e.g. it doesn't really read > > the MSR since there are no outputs > > It's somewhat similar to vmcall()/vmmcall() which are only used to exit > from L2 to L1 (and thus nobody complained that all the register values > are random) and not issue a hypercall and return some value. Sort of. VMCALL/VMMCALL are unique in that they have no meaning (ignoring VMX's STM) other than what is given to them by the hypervisor/software on VM-Exit. RDMSR on the other hand (and literally every other instruction), has architecturally defined behavior and thus expectations beyond generating a VM-Exit. I do think we should clean up the VMCALL/VMMCALL code to remove the clobbers if/when the VM-Enter/VM-Exit sequences are fixed, and maybe make them more generic, e.g. to allow reusing helpers for L1 and L2. But, because the meaning of VMCALL/VMMCALL is software-defined, we'll always need a selftests specific L2=>L1 hypercall, e.g. to ensure L0 forwards the hypercall to L1.
