On Tue, May 30, 2023, Like Xu wrote: > From: Like Xu <likexu@xxxxxxxxxxx> > > Return #GP if KVM user space attempts to set a reserved bit for guest. It's not a #GP, it's simply an error. > If the user space sets reserved bits when restoring the MSR_CORE_ > PERF_GLOBAL_STATUS register, these bits will be accidentally returned > when the guest runs a read access to this register, and cannot be cleared > up inside the guest, which makes the guest's PMI handler very confused. > > Note, reusing global_ovf_ctrl_mask as global_status_mask will be broken > if KVM supports higher versions of Intel arch pmu. > > Signed-off-by: Like Xu <likexu@xxxxxxxxxxx> > --- > arch/x86/kvm/vmx/pmu_intel.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/arch/x86/kvm/vmx/pmu_intel.c b/arch/x86/kvm/vmx/pmu_intel.c > index 1f9c3e916a21..343b3182b7f4 100644 > --- a/arch/x86/kvm/vmx/pmu_intel.c > +++ b/arch/x86/kvm/vmx/pmu_intel.c > @@ -399,7 +399,11 @@ static int intel_pmu_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info) > reprogram_fixed_counters(pmu, data); > break; > case MSR_CORE_PERF_GLOBAL_STATUS: > - if (!msr_info->host_initiated) > + /* > + * Caution, the assumption here is that some of the bits (such as > + * ASCI, CTR_FREEZE, and LBR_FREEZE) are not yet supported by KVM. > + */ A comment wasn't what I had in mind when I objected to "good enough"[*]. Luckily, there's no need to add another mask. After rereading the SDM, there isn't actually a divergence between GLOBAL_STATUS and GLOBAL_OVF_CTRL, Intel just renamed GLOBAL_OVF_CTRL to GLOBAL_STATUS_RESET and for some asinine reason, added separate entries in the architectural MSRs table instead of adding a redirect. I'll post and slot in a patch to do s/global_ovf_ctrl_mask/global_status, along with a comment explaining the rename and how the "reset" MSR is always tied to the status MSR, regardless of what it's named. [*] https://lore.kernel.org/all/37a18b89-c0c3-4c88-7f07-072573ac0c92@xxxxxxxxx
