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

[Hao Peng]

On Tue, Sep 7, 2021 at 1:36 PM Pawan Gupta
<pawan.kumar.gupta@xxxxxxxxxxxxxxx> wrote:
>
> On 07.09.2021 12:39, Hao Peng wrote:
> >On Tue, Sep 7, 2021 at 12:26 PM Xiaoyao Li <xiaoyao.li@xxxxxxxxx> wrote:
> >>
> >> On 9/7/2021 11:40 AM, Hao Peng wrote:
> >> > 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.
> >>
> >> 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.
>
> This suggests that the microcode is old. Can you please share the output
> of below cmds on host and guest:
>
>         $ grep . /sys/devices/system/cpu/vulnerabilities/*
host : not affected
guest: Vulnerable: Clear CPU buffers attempted, no microcode; SMT Host
state unknown.
>         $ lscpu
>         $ grep microcode /proc/cpuinfo | uniq
host: microcode       : 0xd000250
guest: microcode       : 0x1
>         $ cat /proc/cmdline
There are no command line parameters for tsx both host and guest.
>
> Thanks,
> Pawan