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

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Message-ID: <20210907230738.j6j32zvyfpr37qw6@gupta-dev2.localdomain>
Date:   Tue, 7 Sep 2021 16:07:38 -0700
From:   Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
To:     Hao Peng <flyingpenghao@...il.com>
Cc:     Xiaoyao Li <xiaoyao.li@...el.com>, Borislav Petkov <bp@...en8.de>,
        tglx@...utronix.de, mingo@...hat.com, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] x86/tsx: clear RTM and HLE when MSR_IA32_TSX_CTRL is not
 supported

On 07.09.2021 14:56, Hao Peng wrote:
>On Tue, Sep 7, 2021 at 1:36 PM Pawan Gupta
><pawan.kumar.gupta@...ux.intel.com> wrote:
>>
>> On 07.09.2021 12:39, Hao Peng wrote:
>> >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.
>>
>> 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.

This would mean TAA_NO is not being exported to guest. Most likely qemu
needs to be patched for the CPU configuration you are using.

Thanks,
Pawan