linux-kernel - Re: [PATCH] x86/tsx: clear RTM and HLE when MSR_IA32_TSX

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Date:   Tue, 7 Sep 2021 12:39:03 +0800
From:   Hao Peng <flyingpenghao@...il.com>
To:     Xiaoyao Li <xiaoyao.li@...el.com>
Cc:     Borislav Petkov <bp@...en8.de>, tglx@...utronix.de,
        mingo@...hat.com, x86@...nel.org, linux-kernel@...r.kernel.org,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
Subject: Re: [PATCH] x86/tsx: clear RTM and HLE when MSR_IA32_TSX_CTRL is not supported

On Tue, Sep 7, 2021 at 12:26 PM Xiaoyao Li <xiaoyao.li@...el.com> wrote:
>
> On 9/7/2021 11:40 AM, Hao Peng wrote:
> > On Tue, Sep 7, 2021 at 10:56 AM Xiaoyao Li <xiaoyao.li@...el.com> wrote:
> >>
> >> On 9/7/2021 10:35 AM, Hao Peng wrote:
> >>> On Tue, Sep 7, 2021 at 10:08 AM Xiaoyao Li <xiaoyao.li@...el.com> wrote:
> >>>>
> >>>> On 9/7/2021 9:47 AM, Hao Peng wrote:
> >>>>> On Mon, Sep 6, 2021 at 5:30 PM Borislav Petkov <bp@...en8.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@...cent.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);
> >>>>
> >>>> 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.
>
> What's the output of 'cat
> /sys/devices/system/cpu/vulnerabilities/tsx_async_abort' on your guest?
>
Vulnerable: Clear CPU buffers attempted, no microcode; SMT Host state unknown.
> > Thanks.
> >> And the Patch itself makes no sense.
> >>
> >>>>> Thanks.
> >>>>>> --
> >>>>>> Regards/Gruss,
> >>>>>>        Boris.
> >>>>>>
> >>>>>> https://people.kernel.org/tglx/notes-about-netiquette
> >>>>
> >>
>