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From: Josh Poimboeuf <jpoimboe@redhat.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: "Juri Lelli" <juri.lelli@redhat.com>,
	linux-hyperv@vger.kernel.org,
	"Daniel Lezcano" <daniel.lezcano@linaro.org>,
	"Wanpeng Li" <wanpengli@tencent.com>,
	kvm@vger.kernel.org, "VMware, Inc." <pv-drivers@vmware.com>,
	virtualization@lists.linux-foundation.org,
	"Ben Segall" <bsegall@google.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	"Boris Ostrovsky" <boris.ostrovsky@oracle.com>,
	"Wei Liu" <wei.liu@kernel.org>,
	"Stefano Stabellini" <sstabellini@kernel.org>,
	"Stephen Hemminger" <sthemmin@microsoft.com>,
	"Joerg Roedel" <joro@8bytes.org>,
	x86@kernel.org, "Ingo Molnar" <mingo@redhat.com>,
	"Mel Gorman" <mgorman@suse.de>,
	xen-devel@lists.xenproject.org,
	"Haiyang Zhang" <haiyangz@microsoft.com>,
	"Steven Rostedt" <rostedt@goodmis.org>,
	"Borislav Petkov" <bp@alien8.de>,
	luto@kernel.org, "Vincent Guittot" <vincent.guittot@linaro.org>,
	"Thomas Gleixner" <tglx@linutronix.de>,
	"Dietmar Eggemann" <dietmar.eggemann@arm.com>,
	"Jim Mattson" <jmattson@google.com>,
	"Jürgen Groß" <jgross@suse.com>,
	linux-kernel@vger.kernel.org,
	"Sean Christopherson" <sean.j.christopherson@intel.com>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Daniel Bristot de Oliveira" <bristot@redhat.com>
Subject: Re: [PATCH v2 00/12] x86: major paravirt cleanup
Date: Wed, 16 Dec 2020 10:56:05 -0600	[thread overview]
Message-ID: <20201216165605.4h5q7os5dutjgdqi@treble> (raw)
In-Reply-To: <20201216084059.GL3040@hirez.programming.kicks-ass.net>

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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  reply	other threads:[~2020-12-16 16:56 UTC|newest]

Thread overview: 45+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-11-20 11:46 [PATCH v2 00/12] x86: major paravirt cleanup Juergen Gross via Virtualization
2020-11-20 11:46 ` [PATCH v2 03/12] x86/pv: switch SWAPGS to ALTERNATIVE Juergen Gross via Virtualization
2020-11-27 11:31   ` Borislav Petkov
2020-12-09 21:07   ` Thomas Gleixner
2020-11-20 11:46 ` [PATCH v2 04/12] x86/xen: drop USERGS_SYSRET64 paravirt call Juergen Gross via Virtualization
2020-12-02 12:32   ` Borislav Petkov
2020-12-02 14:48     ` Jürgen Groß via Virtualization
2020-12-02 17:08       ` Borislav Petkov
2020-11-20 11:46 ` [PATCH v2 05/12] x86: rework arch_local_irq_restore() to not use popf Juergen Gross via Virtualization
2020-11-20 11:59   ` Peter Zijlstra
2020-11-20 12:05     ` Jürgen Groß via Virtualization
2020-11-22  6:55     ` Jürgen Groß via Virtualization
2020-11-22 21:44       ` Andy Lutomirski
2020-11-23  5:21         ` Jürgen Groß via Virtualization
2020-11-23 15:15           ` Andy Lutomirski
2020-12-09 13:27         ` Mark Rutland
2020-12-09 14:02           ` Mark Rutland
2020-12-09 14:05             ` Jürgen Groß via Virtualization
2020-12-09 18:15     ` Mark Rutland
2020-12-09 18:54       ` Thomas Gleixner
2020-12-10 11:10         ` Mark Rutland
2020-12-10 20:15           ` x86/ioapic: Cleanup the timer_works() irqflags mess Thomas Gleixner
2020-12-11  5:10             ` Jürgen Groß via Virtualization
2020-11-20 11:46 ` [PATCH v2 06/12] x86/paravirt: switch time pvops functions to use static_call() Juergen Gross via Virtualization
2020-11-20 12:01   ` Peter Zijlstra
2020-11-20 12:07     ` Jürgen Groß via Virtualization
2020-11-20 11:46 ` [PATCH v2 08/12] x86/paravirt: remove no longer needed 32-bit pvops cruft Juergen Gross via Virtualization
2020-11-20 12:08   ` Peter Zijlstra
2020-11-20 12:16     ` Jürgen Groß via Virtualization
2020-11-20 11:46 ` [PATCH v2 09/12] x86/paravirt: switch iret pvops to ALTERNATIVE Juergen Gross via Virtualization
2020-11-20 11:46 ` [PATCH v2 10/12] x86/paravirt: add new macros PVOP_ALT* supporting pvops in ALTERNATIVEs Juergen Gross via Virtualization
2020-11-20 11:46 ` [PATCH v2 11/12] x86/paravirt: switch functions with custom code to ALTERNATIVE Juergen Gross via Virtualization
2020-11-20 15:46   ` kernel test robot
2020-11-20 11:46 ` [PATCH v2 12/12] x86/paravirt: have only one paravirt patch function Juergen Gross via Virtualization
2020-11-20 14:18   ` kernel test robot
2020-11-20 12:53 ` [PATCH v2 00/12] x86: major paravirt cleanup Peter Zijlstra
2020-11-23 13:43   ` Peter Zijlstra
2020-12-15 11:42     ` Jürgen Groß via Virtualization
2020-12-15 14:18       ` Peter Zijlstra
2020-12-15 14:54         ` Peter Zijlstra
2020-12-15 15:07           ` Jürgen Groß via Virtualization
2020-12-16  0:38           ` Josh Poimboeuf
2020-12-16  8:40             ` Peter Zijlstra
2020-12-16 16:56               ` Josh Poimboeuf [this message]
2020-12-16 17:58                 ` Peter Zijlstra

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