Re: [Xen-devel] [PATCH 07/10] x86/spec_ctrl: Explicitly set Xen's default MSR_SPEC_CTRL value

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 14.05.18 at 17:39, <wei.liu2@xxxxxxxxxx> wrote:
> On Fri, May 11, 2018 at 11:38:11AM +0100, Andrew Cooper wrote:
>> @@ -417,6 +419,32 @@ void __init init_speculation_mitigations(void)
>>          setup_clear_cpu_cap(X86_FEATURE_NO_XPTI);
>>  
>>      print_details(thunk, caps);
>> +
>> +    /*
>> +     * If MSR_SPEC_CTRL is available, apply Xen's default setting and 
>> discard
>> +     * any firmware settings.  For performance reasons on native hardware, 
>> we
>> +     * delay applying non-zero settings until after dom0 has been 
>> constructed.
>> +     */
>> +    if ( boot_cpu_has(X86_FEATURE_IBRSB) )
>> +    {
>> +        bsp_delay_spec_ctrl = !cpu_has_hypervisor && default_xen_spec_ctrl;
>> +
> 
> Why is cpu_has_hypervisor needed here?  This should help nested case as
> well. And it wouldn't make the setup less secure, right?

Ah, yes, Andrew, this should indeed be explained in at least one of comment
or commit message.

Jan



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