Re: [Xen-devel] [PATCH for-4.11] x86: Use spec_ctrl_{enter, exit}_idle() in the S3/S5 path

["Jan Beulich" <JBeulich@xxxxxxxx>]

>>> On 18.04.18 at 18:27, <andrew.cooper3@xxxxxxxxxx> wrote:
> On 18/04/18 17:14, Jan Beulich wrote:
>>>>> On 18.04.18 at 18:02, <andrew.cooper3@xxxxxxxxxx> wrote:
>>> On 18/04/18 16:43, Jan Beulich wrote:
>>>>>>> On 18.04.18 at 12:43, <andrew.cooper3@xxxxxxxxxx> wrote:
>>>>> This avoids opencoding the functionality (and missing one bit of it), and 
>>>>> and
>>>>> some comments explaining what is going on.
>>>> Missing which bit of it? The MSR writes aren't strictly necessary afaict, 
>>>> and
>>>> functionally clearing bti_ist_info is all that's needed for the entry path 
>>>> of
>>>> interest, while clearing use_shadow_spec_ctrl is all that's needed for the
>>>> exit-to-Xen path. Hence I'm don't see (yet) what bug it is you think this
>>>> fixes.
>>> It is expected that we don't hand off control to the firmware in cases
>>> like this with the mitigations in place.  Here, it doesn't actually
>>> matter too much, but there is no point having the mitigations in effect
>>> when we're the final CPU and trying to shut down.
>> With an improved description the patch can certainly have my R-b; the
>> code change itself is clearly fine with me.
> 
> How about:
> 
> The main purpose of this patch is to avoid opencoding the recovery logic
> at the end, but also has the positive side effect of relaxing the
> SPEC_CTRL mitigations when working to shut the final CPU down.

Much better. With that
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

Jan



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