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

[Hao Peng <flyingpenghao@gmail.com>]

On Mon, Sep 6, 2021 at 5:30 PM Borislav Petkov <bp@alien8.de> 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@tencent.com>
> > ---
> >  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);
> >                 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.
Thanks.
> --
> Regards/Gruss,
>     Boris.
>
> https://people.kernel.org/tglx/notes-about-netiquette