Re: [Xen-devel] [PATCH v8 13/17] x86/boot: Calculate the most appropriate BTI mitigation to use

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

On 16/01/18 14:10, Boris Ostrovsky wrote:
> On 01/12/2018 01:01 PM, Andrew Cooper wrote:
>>  
>> +    if ( boot_cpu_has(X86_FEATURE_IBRSB) )
>> +    {
>> +        /*
>> +         * Even if we've chosen to not have IBRS set in Xen context, we 
>> still
>> +         * need the IBRS entry/exit logic to virtualise IBRS support for
>> +         * guests.
>> +         */
>> +        if ( ibrs )
>> +            setup_force_cpu_cap(X86_FEATURE_XEN_IBRS_SET);
>> +        else
>> +            setup_force_cpu_cap(X86_FEATURE_XEN_IBRS_CLEAR);
>> +    }
>>
> Are you going to add support for Intel's "Enhanced IBRS" (I think that's
> what they call the "always on" mode")?

I'm not going to touch IBRS_ATT mode until I've got an SDP to develop
against.

Given how many times the IBRS_ATT spec has changed already, I have
little confidence that it will remain unchanged right to the eventual
hardware arrives.

~Andrew

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