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Date:   Mon, 18 Jan 2021 14:35:03 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Like Xu <like.xu@linux.intel.com>
Cc:     kbuild-all@lists.01.org, clang-built-linux@googlegroups.com,
        Ingo Molnar <mingo@redhat.com>,
        Arnaldo Carvalho de Melo <acme@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Borislav Petkov <bp@alien8.de>, x86@kernel.org,
        linux-kernel@vger.kernel.org, Jason Baron <jbaron@akamai.com>,
        Josh Poimboeuf <jpoimboe@redhat.com>,
        kernel test robot <lkp@intel.com>
Subject: Re: [PATCH] x86/perf: Use static_call for x86_pmu.guest_get_msrs
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References: <20210118072151.44481-1-like.xu@linux.intel.com>
 <202101182008.jQybUDa0-lkp@intel.com>
 <a82754e7-9a2d-7ab4-466d-fc0d51a3b7f2@linux.intel.com>
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On Mon, Jan 18, 2021 at 09:05:06PM +0800, Like Xu wrote:
> I guess this fix will silence the compiler error,
> and v2 will be sent after the local 0day test passes.

I think there's also a problem where you don't assign a function at all.

I think you want something like

	if (!x86_pmu.guest_get_msr)
		x86_pmu.guest_get_msr = guest_get_msr_nop;

right before x86_pmu_static_call_update();

And then have it be something like:

static void *guest_et_msr_nop(int *nr)
{
	*nr = 0;
	return NULL;
}

and then you can reduce the entire thing to:

struct perf_guest_switch_msr *perf_guest_get_msrs(int *nr)
{
	return static_call(x86_pmu_guest_get_msrs)(nr);
}