Re: [PATCH v2] target/i386: Add Snowridge-v2 (noMPX) CPU model

[Xiaoyao Li <xiaoyao.li@intel.com>]

On 10/12/2019 9:21 AM, Eduardo Habkost wrote:
> On Sat, Oct 12, 2019 at 09:15:56AM +0800, Xiaoyao Li wrote:
>> On 10/12/2019 2:21 AM, Eduardo Habkost wrote:
>>> On Fri, Oct 11, 2019 at 10:53:49PM +0800, Xiaoyao Li wrote:
>>>> Add new version of Snowridge CPU model that removes MPX feature.
>>>>
>>>> MPX support is being phased out by Intel. GCC has dropped it, Linux kernel
>>>> and kvm are also going to do that in the future.
>>>>
>>>> Signed-off-by: Xiaoyao Li <xiaoyao.li@intel.com>
>>>> ---
>>>> Changes in v2:
>>>>       - Use CPU model versioning mechanism instead of machine-type compat
>>>> ---
>>>>    target/i386/cpu.c | 13 +++++++++++++
>>>>    1 file changed, 13 insertions(+)
>>>>
>>>> diff --git a/target/i386/cpu.c b/target/i386/cpu.c
>>>> index 44f1bbdcac76..27b0a17b46a8 100644
>>>> --- a/target/i386/cpu.c
>>>> +++ b/target/i386/cpu.c
>>>> @@ -2793,6 +2793,19 @@ static X86CPUDefinition builtin_x86_defs[] = {
>>>>                CPUID_6_EAX_ARAT,
>>>>            .xlevel = 0x80000008,
>>>>            .model_id = "Intel Atom Processor (SnowRidge)",
>>>> +        .versions = (X86CPUVersionDefinition[]) {
>>>> +            { .version = 1 },
>>>> +            {
>>>> +                .version = 2,
>>>> +                .alias = "Snowridge-noMPX",
>>>
>>> The intention is to stop creating new funny names for CPU model
>>> variations, now, and stick to -v1, -v2, -v3, etc.
>>>
>>> The .alias field is optional, and was added only for
>>> compatibility with the existing -noTSX and -IBRS CPU models.
>>
>> Got it.
>>
>>>> +                .props = (PropValue[]) {
>>>> +                    { "mpx", "off" },
>>>> +                    { "model-id", "Intel Atom Processor (Snowridge, no MPX)" },
>>>
>>> Do you think it's important to report a different model-id?
>>> I would keep it the same and only add mpx=off.
>>
>> I just want to let user know easily the differences between Snowridge-v1 and
>> Snowridge-v2. Unfortunately, it seems ugly.
>>
>> When testing with Cascadelake-Server, it puzzles every time that which one
>> should I choose between Cascadelake-Server-v1 and Cascadelake-Server-v2.
>>  From the output of "-cpu ?", I don't know the differences between them.
>> Everytime I have to go to the source code to see the difference.
>>
>> Maybe there is a way to see/report the differences between different
>> versions of the same CPU model that I just don't know?
> 
> Good point.  I forgot that model-id is also the model description
> in "-cpu ?".
> 
> Well, it doesn't hurt to have a different model-id in v2 that's
> more informative.  Feel free to keep the model-id line in v3.

OK. I will send out the v3 patch keeping the model-id while removing the 
alias.

BTW, do you have better idea to tell the differences among versions of 
the same CPU model?