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From: Jessica Yu <jeyu@kernel.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Dexuan Cui <decui@microsoft.com>, Ingo Molnar <mingo@kernel.org>,
	Daniel Bristot de Oliveira <bristot@redhat.com>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	Josh Poimboeuf <jpoimboe@redhat.com>
Subject: Re: static_branch_enable() does not work from a __init function?
Date: Wed, 16 Dec 2020 13:38:05 +0100	[thread overview]
Message-ID: <20201216123805.GB13751@linux-8ccs> (raw)
In-Reply-To: <20201216092649.GM3040@hirez.programming.kicks-ass.net>

+++ Peter Zijlstra [16/12/20 10:26 +0100]:
>On Wed, Dec 16, 2020 at 03:54:29AM +0000, Dexuan Cui wrote:
>> PS, I originally found: in arch/x86/kvm/vmx/vmx.c: vmx_init(), it looks
>> like the line "static_branch_enable(&enable_evmcs);" does not take effect
>> in a v5.4-based kernel, but does take effect in the v5.10 kernel in the
>> same x86-64 virtual machine on Hyper-V, so I made the above test module
>> to test static_branch_enable(), and found that static_branch_enable() in
>> the test module does not work with both v5.10 and my v5.4 kernel, if the
>> __init marker is used.

By the way, it probably works now because there was a workaround
merged in v5.10, that mentions this very issue:

commit 064eedf2c50f692088e1418c553084bf9c1432f8
Author: Vitaly Kuznetsov <vkuznets@redhat.com>
Date:   Wed Oct 14 16:33:46 2020 +0200

    KVM: VMX: eVMCS: make evmcs_sanitize_exec_ctrls() work again

    It was noticed that evmcs_sanitize_exec_ctrls() is not being executed
    nowadays despite the code checking 'enable_evmcs' static key looking
    correct. Turns out, static key magic doesn't work in '__init' section
    (and it is unclear when things changed) but setup_vmcs_config() is called
    only once per CPU so we don't really need it to. Switch to checking
    'enlightened_vmcs' instead, it is supposed to be in sync with
    'enable_evmcs'.

    Opportunistically make evmcs_sanitize_exec_ctrls '__init' and drop unneeded
    extra newline from it.

    Reported-by: Yang Weijiang <weijiang.yang@intel.com>
    Signed-off-by: Vitaly Kuznetsov <vkuznets@redhat.com>
    Message-Id: <20201014143346.2430936-1-vkuznets@redhat.com>
    Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>


      parent reply	other threads:[~2020-12-16 12:39 UTC|newest]

Thread overview: 20+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-12-16  3:54 static_branch_enable() does not work from a __init function? Dexuan Cui
2020-12-16  9:26 ` Peter Zijlstra
2020-12-16 10:59   ` Peter Zijlstra
2020-12-16 13:30     ` [RFC][PATCH] jump_label/static_call: Add MAINTAINERS Peter Zijlstra
2020-12-16 13:42       ` Peter Zijlstra
2020-12-16 14:23         ` Steven Rostedt
2020-12-16 16:19         ` Josh Poimboeuf
2020-12-16 16:19         ` Ard Biesheuvel
2020-12-16 21:16         ` Jason Baron
2020-12-18 16:02       ` [tip: locking/urgent] " tip-bot2 for Peter Zijlstra
2020-12-16 13:54     ` [PATCH] jump_label: Fix usage in module __init Peter Zijlstra
2020-12-16 16:36       ` Josh Poimboeuf
2020-12-18 16:02       ` [tip: locking/urgent] " tip-bot2 for Peter Zijlstra
2020-12-16 20:45     ` static_branch_enable() does not work from a __init function? Dexuan Cui
2020-12-16 11:55   ` Jessica Yu
2020-12-16 12:47     ` Peter Zijlstra
2020-12-16 13:10       ` Jessica Yu
2020-12-16 13:23         ` Peter Zijlstra
2020-12-16 13:27           ` Jessica Yu
2020-12-16 12:38   ` Jessica Yu [this message]

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