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

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Message-ID: <c04ecd71-a7d5-9adb-e306-35ea474e6fe1@suse.com>
Date:   Wed, 9 Aug 2017 11:55:35 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Peter Zijlstra <peterz@...radead.org>
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 09/08/17 11:35, Peter Zijlstra wrote:
> 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.

I don't see why this couldn't be changed.


Juergen