linux-kernel - Re: [PATCH v2 23/24] x86/xen: Rework the xen_{cpu,irq,mmu}

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Date:   Thu, 24 Jun 2021 14:12:51 +0200
From:   Juergen Gross <jgross@...e.com>
To:     Peter Zijlstra <peterz@...radead.org>, jpoimboe@...hat.com,
        tglx@...utronix.de
Cc:     linux-kernel@...r.kernel.org, joro@...tes.org,
        boris.ostrovsky@...cle.com, x86@...nel.org, mbenes@...e.com,
        rostedt@...dmis.org, dvyukov@...gle.com, elver@...gle.com
Subject: Re: [PATCH v2 23/24] x86/xen: Rework the xen_{cpu,irq,mmu}_ops[]
 arrays

On 24.06.21 11:41, Peter Zijlstra wrote:
> In order to allow objtool to make sense of all the various paravirt
> functions, it needs to either parse whole pv_ops[] tables, or observe
> individual assignments in the form:
> 
>    bf87:       48 c7 05 00 00 00 00 00 00 00 00        movq   $0x0,0x0(%rip)
>      bf92 <xen_init_spinlocks+0x5f>
>      bf8a: R_X86_64_PC32     pv_ops+0x268
> 
> As is, xen_cpu_ops[] is at offset +0 in pv_ops[] and could thus be
> parsed as a 'normal' pv_ops[] table, however xen_irq_ops[] and
> xen_mmu_ops[] are not.
> 
> Worse, both the latter two are compiled into the individual assignment
> for by current GCC, but that's not something one can rely on.
> 
> Therefore, convert all three into full pv_ops[] tables. This has the
> benefit of not needing to teach objtool about the offsets and
> resulting in more conservative code-gen.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

First I was worried by the additional memory consumption, but as the
modified tables are all tagged to be __init I don't think this matters.

So:

Reviewed-by: Juergen Gross <jgross@...e.com>


Juergen

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