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Re: [PATCH v2 00/12] x86: major paravirt cleanup
- To: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
- From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
- Date: Wed, 16 Dec 2020 10:56:05 -0600
- Cc: Jürgen Groß <jgross@xxxxxxxx>, xen-devel@xxxxxxxxxxxxxxxxxxxx, x86@xxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx, virtualization@xxxxxxxxxxxxxxxxxxxxxxxxxx, linux-hyperv@xxxxxxxxxxxxxxx, kvm@xxxxxxxxxxxxxxx, luto@xxxxxxxxxx, Thomas Gleixner <tglx@xxxxxxxxxxxxx>, Ingo Molnar <mingo@xxxxxxxxxx>, Borislav Petkov <bp@xxxxxxxxx>, "H. Peter Anvin" <hpa@xxxxxxxxx>, Boris Ostrovsky <boris.ostrovsky@xxxxxxxxxx>, Stefano Stabellini <sstabellini@xxxxxxxxxx>, Deep Shah <sdeep@xxxxxxxxxx>, "VMware, Inc." <pv-drivers@xxxxxxxxxx>, "K. Y. Srinivasan" <kys@xxxxxxxxxxxxx>, Haiyang Zhang <haiyangz@xxxxxxxxxxxxx>, Stephen Hemminger <sthemmin@xxxxxxxxxxxxx>, Wei Liu <wei.liu@xxxxxxxxxx>, Paolo Bonzini <pbonzini@xxxxxxxxxx>, Sean Christopherson <sean.j.christopherson@xxxxxxxxx>, Vitaly Kuznetsov <vkuznets@xxxxxxxxxx>, Wanpeng Li <wanpengli@xxxxxxxxxxx>, Jim Mattson <jmattson@xxxxxxxxxx>, Joerg Roedel <joro@xxxxxxxxxx>, Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>, Juri Lelli <juri.lelli@xxxxxxxxxx>, Vincent Guittot <vincent.guittot@xxxxxxxxxx>, Dietmar Eggemann <dietmar.eggemann@xxxxxxx>, Steven Rostedt <rostedt@xxxxxxxxxxx>, Ben Segall <bsegall@xxxxxxxxxx>, Mel Gorman <mgorman@xxxxxxx>, Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
- Delivery-date: Wed, 16 Dec 2020 16:56:48 +0000
- List-id: Xen developer discussion <xen-devel.lists.xenproject.org>
On Wed, Dec 16, 2020 at 09:40:59AM +0100, Peter Zijlstra wrote:
> > So much algorithm.
>
> :-)
>
> It's not really hard, but it has a few pesky details (as always).
It really hurt my brain to look at it.
> > Could we make it easier by caching the shared
> > per-alt-group CFI state somewhere along the way?
>
> Yes, but when I tried it grew the code required. Runtime costs would be
> less, but I figured that since alternatives are typically few and small,
> that wasn't a real consideration.
Aren't alternatives going to be everywhere now with paravirt using them?
> That is, it would basically cache the results of find_alt_unwind(), but
> you still need find_alt_unwind() to generate that data, and so you gain
> the code for filling and using the extra data structure.
>
> Yes, computing it 3 times is naf, but meh.
Haha, I loved this sentence.
> > Thoughts? This is all theoretical of course, I could try to do a patch
> > tomorrow.
>
> No real objection, I just didn't do it because 1) it works, and 2) even
> moar lines.
I'm kind of surprised it would need moar lines. Let me play around with
it and maybe I'll come around ;-)
--
Josh
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