Re: [PATCH] x86/tsx: clear RTM and HLE when MSR_IA32_TSX_CTRL is not supported

[Xiaoyao Li]

On 9/7/2021 9:47 AM, Hao Peng wrote:
> On Mon, Sep 6, 2021 at 5:30 PM Borislav Petkov <bp@xxxxxxxxx> wrote:
> > On Mon, Sep 06, 2021 at 10:46:05AM +0800, Hao Peng wrote:
> > > If hypervisor does not support MSR_IA32_TSX_CTRL, but guest supports
> > > RTM and HLE features, it will affect TAA mitigation.
> > >
> > > Signed-off-by: Peng Hao <flyingpeng@xxxxxxxxxxx>
> > > ---
> > >   arch/x86/kernel/cpu/tsx.c | 7 +++++++
> > >   1 file changed, 7 insertions(+)
> > >
> > > diff --git a/arch/x86/kernel/cpu/tsx.c b/arch/x86/kernel/cpu/tsx.c
> > > index 9c7a5f049292..5e852c14fef2 100644
> > > --- a/arch/x86/kernel/cpu/tsx.c
> > > +++ b/arch/x86/kernel/cpu/tsx.c
> > > @@ -122,6 +122,13 @@ void __init tsx_init(void)
> > >
> > >          if (!tsx_ctrl_is_supported()) {
> > >                  tsx_ctrl_state = TSX_CTRL_NOT_SUPPORTED;
> > > +
> > > +               /* If hypervisor does not support MSR_IA32_TSX_CTRL emulation,
> > > +                * but guest supports RTM and HLE features, it will affect TAA
> > > +                * （tsx_async_abort）mitigation.
> > > +                */
> > > +               setup_clear_cpu_cap(X86_FEATURE_RTM);
> > > +               setup_clear_cpu_cap(X86_FEATURE_HLE);

anyway, IMHO, we shouldn't do anything here for TAA. It should be in 
taa_select_mitigation()

> > >                  return;
> > >          }
> >
> > How does that even happen - the hypervisor does not support the MSR but
> > "guest supports" TSX features?!
> >
> > I guess the guest is detecting it wrong.
> >
> > What hypervisor, what guest, how do I reproduce?
> hypervisor is kvm, guest is linux too.
> > Please give full details.
> The host I used is kernel-5.4, and guest is kernel-5.13.
> MSR_IA32_TSX_CTRL is exposed
> to guest and guest to support RTM and HLE features, no direct
> dependence. at the qemu I
> started guest with -cpu host-model.
> I have viewed the code of kernel-5.4, and MSR_IA32_TSX_CTRL is not
> exposed to guest.

Does guest see TAA_NO bit?

> Thanks.
> > --
> > Regards/Gruss,
> >      Boris.
> >
> > https://people.kernel.org/tglx/notes-about-netiquette