On Fri, Jan 29, 2021, Paolo Bonzini wrote: > diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c > index 76bce832cade..15733013b266 100644 > --- a/arch/x86/kvm/x86.c > +++ b/arch/x86/kvm/x86.c > @@ -1401,7 +1401,7 @@ static u64 kvm_get_arch_capabilities(void) > * This lets the guest use VERW to clear CPU buffers. This comment be updated to call out the new TSX_CTRL behavior. /* * On TAA affected systems: * - nothing to do if TSX is disabled on the host. * - we emulate TSX_CTRL if present on the host. * This lets the guest use VERW to clear CPU buffers. */ > */ > if (!boot_cpu_has(X86_FEATURE_RTM)) > - data &= ~(ARCH_CAP_TAA_NO | ARCH_CAP_TSX_CTRL_MSR); > + data &= ~ARCH_CAP_TAA_NO; Hmm, simply clearing TSX_CTRL will only preserve the host value. Since ARCH_CAPABILITIES is unconditionally emulated by KVM, wouldn't it make sense to unconditionally expose TSX_CTRL as well, as opposed to exposing it only if it's supported in the host? I.e. allow migrating a TSX-disabled guest to a host without TSX. Or am I misunderstanding how TSX_CTRL is checked/used? > else if (!boot_cpu_has_bug(X86_BUG_TAA)) > data |= ARCH_CAP_TAA_NO; > > -- > 2.26.2 >
