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Re: [PATCH] x86/spec-ctrl: Skip RSB overwriting when safe to do so
- To: Jan Beulich <jbeulich@xxxxxxxx>
- From: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- Date: Wed, 25 Aug 2021 16:11:17 +0100
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- Cc: Roger Pau Monné <roger.pau@xxxxxxxxxx>, Wei Liu <wl@xxxxxxx>, Xen-devel <xen-devel@xxxxxxxxxxxxxxxxxxxx>
- Delivery-date: Wed, 25 Aug 2021 15:11:34 +0000
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On 25/08/2021 15:36, Jan Beulich wrote:
> On 25.08.2021 14:12, Andrew Cooper wrote:
>> On 24/08/2021 14:04, Jan Beulich wrote:
>>> On 19.08.2021 18:26, Andrew Cooper wrote:
>>>> In some configurations, it is safe to not overwrite the RSB on entry to
>>>> Xen.
>>>> Both Intel and AMD have guidelines in this area, because of the performance
>>>> difference it makes for native kernels.
>>> I don't think I've come across AMD's guidelines - would you happen to
>>> have a pointer?
>> APM Vol2 3.2.9 "Speculation Control MSRs"
>>
>> The information about SMEP is in the final paragraph before describing
>> MSR_SPEC_CTRL.STIBP.
> Ah yes, thanks. Still need to get used to this now being in the PM rather
> than in one or more separate docs. I now recall reading through this.
I'm still pushing Intel to add a section/chapter to the SDM, because
this is is all architectural functionality and interfaces.
~Andrew
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