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Re: [Xen-devel] Backports to 4.13

On 06.03.2020 14:52, Andrew Cooper wrote:
> You've recently backported 328dd238da "x86/sm{e, a}p: do not enable
> SMEP/SMAP in PV shim by default on AMD", but have missed 5de961d9c097
> "x86: do not enable global pages when virtualized on AMD or Hygon
> hardware" and b041709c369b "x86/pv: Fix `global-pages` to match the
> documentation".

I've queued these up, albeit ...

> The former is pretty useless without the other two, because you're
> taking out the security feature without gaining the majority performance
> win from avoiding VMexits due to CR4 traps.

... I'm unconvinced of this - avoiding SMEP/SMAP alone already
eliminates a number of CR4 writes afaict.

> Depending on the view of other PV shim usability issues, 6dd95b02ea27
> and f9dee1f945eb regarding vtsc make a large difference and should be
> considered.

I've queued the latter, but the former doesn't really look like
backporting material to me.

> e2d1254f5af2 is a bugfix which needs backporting to fix AMD S3 and
> kexec, as well as pv shim.

Queued as well.

> 188f479de4b7 and 005de45c887e are both core scheduling bugfixes and
> should be considered, even if they are a little too fresh right at the
> moment.

"Freshness" is not an issue imo. They've passed the push gate on
master, and I wouldn't get around to apply them right away anyway.
With these it's just the typical situation for features that are
still "experimental" or alike - I'm never really certain whether
it's better to pull in such fixes (and have more code churn) or
to leave them out. And explicit request like this one of yours
helps take a decision.

> On the tools side of things, f50a4f6e244c aafae0e800e9 2a62c22715bf
> d79cc6bc2bac 0729830cc425 are all bugs in CPUID and/or migration.  "Fix
> HVM_PARAM_PAE_ENABLED handling" is only for 4.13, whereas all the others
> are back to 4.7 (technically speaking).

I'll (obviously) leave these to Ian.


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