linux-kernel - Re: [PATCH v4 1/2] x86/unwind: add ORC unwinder

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Date:   Wed, 9 Aug 2017 11:35:11 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Juergen Gross <jgross@...e.com>
Cc:     Andy Lutomirski <luto@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        "Levin, Alexander (Sasha Levin)" <alexander.levin@...izon.com>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "live-patching@...r.kernel.org" <live-patching@...r.kernel.org>,
        Jiri Slaby <jslaby@...e.cz>, Ingo Molnar <mingo@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>, Mike Galbraith <efault@....de>
Subject: Re: [PATCH v4 1/2] x86/unwind: add ORC unwinder

On Wed, Aug 09, 2017 at 11:24:07AM +0200, Juergen Gross wrote:
> On 09/08/17 11:16, Peter Zijlstra wrote:
> > On Wed, Aug 09, 2017 at 10:49:43AM +0200, Juergen Gross wrote:
> >>> ALTERNATIVE "pushfq; popq %rax", "callq *pv_irq_ops.save_fl",
> >>> X86_FEATURE_GODDAMN_PV_IRQ_OPS
> >>
> >> You are aware that at least some of the Xen irq pvops functionality is
> >> patched inline? Your modification would slow down pv guests quite a
> >> bit, I guess.
> > 
> > Where does that live? I know of the inline patching for native, but
> > didn't know the guests did any of that too.
> 
> See arch/x86/xen/enlighten_pv.c xen_patch().

'obvious' name that :-) I see that the actual code that's patched in
lives in xen-asm.S which unlike the native case doesn't appear to have
its own section. So that might make things even more difficult.