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Re: [PATCH] x86/spec-ctrl: Skip RSB overwriting when safe to do so
- To: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
- From: Jan Beulich <jbeulich@xxxxxxxx>
- Date: Wed, 25 Aug 2021 16:36:17 +0200
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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 14:36:33 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
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.
Jan
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