On Mon, Mar 27, 2023, Jim Mattson wrote: > On Sun, Mar 26, 2023 at 8:33 PM Xiaoyao Li <xiaoyao.li@xxxxxxxxx> wrote: > > > > On 3/22/2023 9:14 AM, Sean Christopherson wrote: > > > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > > > index c83ec88da043..3c58dbae7b4c 100644 > > > --- a/arch/x86/kvm/x86.c > > > +++ b/arch/x86/kvm/x86.c > > > @@ -3628,6 +3628,18 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info) > > > > > > wrmsrl(MSR_IA32_PRED_CMD, PRED_CMD_IBPB); > > > break; > > > + case MSR_IA32_FLUSH_CMD: > > > + if (!msr_info->host_initiated && > > > + !guest_cpuid_has(vcpu, X86_FEATURE_FLUSH_L1D)) > > > + return 1; > > > + > > > + if (!boot_cpu_has(X86_FEATURE_FLUSH_L1D) || (data & ~L1D_FLUSH)) > > > + return 1; > > > + if (!data) > > > + break; > > > + > > > + wrmsrl(MSR_IA32_FLUSH_CMD, L1D_FLUSH); > > > + break; > > > > Then KVM provides the ability to flush the L1 data cache of host to > > userspace. Can it be exploited to degrade the host performance if > > userspace VMM keeps flushing the L1 data cache? > > The L1D$ isn't very big. A guest could always flush out any previously > cached data simply by referencing its own data. Is the ability to > flush the L1D$ by WRMSR that egregious? Yeah, AFAIK RDT and the like only provide QoS controls for L3, so L1 is fair game.
