RE: [PATCH v2] target/i386: Restore TSX features with taa-no

[Duan, Zhenzhong]

>-----Original Message-----
>From: Li, Xiaoyao <xiaoyao.li@intel.com>
>Sent: Friday, July 15, 2022 9:14 AM
>To: Paolo Bonzini <pbonzini@redhat.com>; Duan, Zhenzhong
><zhenzhong.duan@intel.com>; qemu-devel@nongnu.org
>Cc: ehabkost@redhat.com; Ma, XiangfeiX <xiangfeix.ma@intel.com>;
>Christopherson,, Sean <seanjc@google.com>
>Subject: Re: [PATCH v2] target/i386: Restore TSX features with taa-no
>
>On 7/14/2022 3:59 PM, Paolo Bonzini wrote:
>> On 7/14/22 07:36, Zhenzhong Duan wrote:
>>> On ICX-2S2 host, when run L2 guest with both L1/L2 using
>>> Icelake-Server-v3
>>> or above, we got below warning:
>>>
>>> "warning: host doesn't support requested feature: MSR(10AH).taa-no
>>> [bit 8]"
>>>
>>> This is because L1 KVM doesn't expose taa-no to L2 if RTM is
>>> disabled, then starting L2 qemu triggers the warning.
>>>
>>> Fix it by restoring TSX features in Icelake-Server-v3, which may also
>>> help guest performance if host isn't susceptible to TSX Async Abort
>>> (TAA) vulnerabilities.
>>>
>>> Fixes: d965dc35592d ("target/i386: Add ARCH_CAPABILITIES related bits
>>> into Icelake-Server CPU model")
>>> Tested-by: Xiangfei Ma <xiangfeix.ma@intel.com>
>>> Signed-off-by: Zhenzhong Duan <zhenzhong.duan@intel.com>
>>> ---
>>> v2: Rewrite commit message
>>
>> Why wouldn't the fix be (in an Icelake-Server-v4 model) to remove taa-no?
>
>Production Icelake silicon should have the taa-no set, that's the reason taa-no
>was added in v3 model.
>
>When taa-no presents, it's safe to bring TSX features back.
>
>I'm wondering if we need a new version (v7) for this change.

Ping. Any further suggestion on which way to go ahead? Thanks

Zhenzhong