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

[Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>]

On 01/16/2018 09:13 AM, Andrew Cooper wrote:
> 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.

I don't know if you are aware of it (I learned about this doc on Sunday) but

https://software.intel.com/sites/default/files/managed/c5/63/336996-Speculative-Execution-Side-Channel-Mitigations.pdf

(Not part of the SDM but still, an official specification. For a change.)

-boris

-boris

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