linux-kernel - Re: [PATCH 0/2] x86/context-tracking: Remove last remaining calls to exception_enter/exception

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Message-ID: <20200106155819.GC26097@lenoir>
Date:   Mon, 6 Jan 2020 16:58:20 +0100
From:   Frederic Weisbecker <frederic@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Wanpeng Li <wanpengli@...cent.com>,
        Borislav Petkov <bp@...en8.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Sean Christopherson <sean.j.christopherson@...el.com>,
        Ingo Molnar <mingo@...hat.com>,
        Jim Mattson <jmattson@...gle.com>,
        Joerg Roedel <joro@...tes.org>,
        Andy Lutomirski <luto@...nel.org>,
        Vitaly Kuznetsov <vkuznets@...hat.com>
Subject: Re: [PATCH 0/2] x86/context-tracking: Remove last remaining calls to
 exception_enter/exception_exit()

On Mon, Jan 06, 2020 at 04:05:46PM +0100, Peter Zijlstra wrote:
> On Fri, Dec 27, 2019 at 05:36:10PM +0100, Frederic Weisbecker wrote:
> > Thanks to the cleanups from Andy Lutomirski over the years, those calls
> > can now be removed. This will allow for nice things in the future for
> > x86 support on full nohz:
> > 
> > * Remove TIF_NOHZ and use a per-cpu switch to enable, disable context
> >   tracking.
> > 
> > * Avoid context tracking on housekeepers.
> > 
> > * Dynamically enable/disable context tracking on CPU on runtime and
> >   therefore allow runtime enable/disable of nohz_full
> > 
> > * Make nohz_full a property of cpuset.
> > 
> > Frederic Weisbecker (2):
> >   x86/context-tracking: Remove exception_enter/exit() from
> >     do_page_fault()
> >   x86/context-tracking: Remove exception_enter/exit() from
> >     KVM_PV_REASON_PAGE_NOT_PRESENT async page fault
> 
> Thanks, these look good to me.
> 
> Did I tell you about my 'TODO' item vs text_poke_sync() ? Basically, we
> can avoid sending the IPI to NOHZ_FULL user CPUs, provided we make their
> enter_from_user_mode() do the sync_core().

Yeah I believe I saw some email about that somewhere. I hope I didn't miss
a patch about that. Anyway, whether past or future patch, I'll happily review that :-)