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

[Hao Peng]

On Tue, Sep 7, 2021 at 10:56 AM Xiaoyao Li <xiaoyao.li@xxxxxxxxx> wrote:
>
> On 9/7/2021 10:35 AM, Hao Peng wrote:
> > On Tue, Sep 7, 2021 at 10:08 AM Xiaoyao Li <xiaoyao.li@xxxxxxxxx> wrote:
> >>
> >> 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?
> >>
> > Guest can't see taa_no, which requires updating qemu to solve. But I think
> > there is a compatibility process here.
>
> Anyway, there should be some existing code in kernel already to handle
> the case that CPUID reports TRM while MSR_IA32_CORE_CAPABILITIES doesn't
> report MSR_TSX_CTRL nor TAA_NO.
>
Can you point out which patches ? At present, guest is kernel-5.13
still has this problem.
Thanks.
> And the Patch itself makes no sense.
>
> >>> Thanks.
> >>>> --
> >>>> Regards/Gruss,
> >>>>       Boris.
> >>>>
> >>>> https://people.kernel.org/tglx/notes-about-netiquette
> >>
>