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

[Duan, Zhenzhong]

>-----Original Message-----
>From: Li, Xiaoyao <xiaoyao.li@intel.com>
>Sent: Friday, July 8, 2022 2:03 PM
>To: Duan, Zhenzhong <zhenzhong.duan@intel.com>; qemu-
>devel@nongnu.org
>Cc: pbonzini@redhat.com; ehabkost@redhat.com; Ma, XiangfeiX
><xiangfeix.ma@intel.com>
>Subject: Re: [PATCH] target/i386: Restore TSX features with taa-no
>
>On 7/8/2022 1:42 PM, Zhenzhong Duan wrote:
>> In L1 kernel side, taa-no is cleared because RTM is disabled which
>> will lead to below warning when starting L2 qemu:
>>
>> "warning: host doesn't support requested feature: MSR(10AH).taa-no [bit
>8]"
>>
>> If host isn't susceptible to TSX Async Abort (TAA) vulnerabilities,
>> exposing TSX to L2 may help performance too.
>
>If L1 doesn't see RTM, how can it expose it to L2?

Sorry, looks my words is confusing. Should be "exposing TSX to guest may help 
performance too"
After patch, both L1 and L2 will see RTM if both are Icelake-Server-v3 or above.

Thanks
Zhenzhong
>
>> 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>
>> ---
>>   target/i386/cpu.c | 3 +++
>>   1 file changed, 3 insertions(+)
>>
>> diff --git a/target/i386/cpu.c b/target/i386/cpu.c index
>> 6a57ef13af86..bda2569c73cc 100644
>> --- a/target/i386/cpu.c
>> +++ b/target/i386/cpu.c
>> @@ -3423,6 +3423,9 @@ static const X86CPUDefinition builtin_x86_defs[]
>= {
>>               {
>>                   .version = 3,
>>                   .props = (PropValue[]) {
>> +                    /* Restore TSX features removed by -v2 above */
>> +                    { "hle", "on" },
>> +                    { "rtm", "on" },
>>                       { "arch-capabilities", "on" },
>>                       { "rdctl-no", "on" },
>>                       { "ibrs-all", "on" },