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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

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.




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