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

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Date:   Tue, 7 Sep 2021 10:56:15 +0800
From:   Xiaoyao Li <xiaoyao.li@...el.com>
To:     Hao Peng <flyingpenghao@...il.com>,
        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 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.

And the Patch itself makes no sense.

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