From nobody Thu Sep 18 21:54:28 2025 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D3E49C001DE for ; Fri, 21 Jul 2023 20:19:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231207AbjGUUT3 (ORCPT ); Fri, 21 Jul 2023 16:19:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38010 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229572AbjGUUTS (ORCPT ); Fri, 21 Jul 2023 16:19:18 -0400 Received: from mail-yb1-xb49.google.com (mail-yb1-xb49.google.com [IPv6:2607:f8b0:4864:20::b49]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 811B835AC for ; Fri, 21 Jul 2023 13:19:08 -0700 (PDT) Received: by mail-yb1-xb49.google.com with SMTP id 3f1490d57ef6-d061f324d64so526865276.1 for ; Fri, 21 Jul 2023 13:19:08 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20221208; t=1689970748; x=1690575548; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:reply-to:from:to:cc:subject:date:message-id:reply-to; bh=8mt2rx9ZLjLB1KoF/SJo016XQ9rXRtE6G9Sw+PvIk2E=; b=46uRXOuIfr0DhaSfjJ1gilpLeWI3SkY0gBhy4/JE8Ffy8aB+wmHHv0eZLbPKwxGf1W zRibu2Q+TOMsOsJJb4OHXHOPphrSRQVtzF5JSYhNBOCF7LUJtPtEWSRYc2JzZ4acAnor /zmJ7rgJese6SY0MTnK9LF9xzGYySIQj6WHl2lAxP+dEQMc/jN7H8FWycEgSVz1jPhiN kHTFjuNTxv4dt/QE31tPp7lm/S5hHzAiuf3QYbCoqwzmHIbVLyemLu2fOiOfokkTKl20 itFUL9M3X8lEkW6ABJkQLWfuSKa41xBM+UYU6HXoNTkiMFGmgDhcqWF7uCFWGdPxsAIv jV9w== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1689970748; x=1690575548; h=cc:to:from:subject:message-id:references:mime-version:in-reply-to :date:reply-to:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=8mt2rx9ZLjLB1KoF/SJo016XQ9rXRtE6G9Sw+PvIk2E=; b=b376PQm6Xfdpm85rM0cqRpxcPkOJPQzw52zmr1Kc7Y1WdecvnFUKYEpf8mlHAbYrwI S2dv/RjwXTyTQJwDOeMaZDqQ/yuSiWyTVwzPYpz6ctKb426wcgBHD4IkFTtEDfQY9UDC +iwxBAxyiUoZobjlkl9keUrq+M8Og7qyXBC5GW/lXrKI/2VhgO1ITjKFFPeTbJYeK8R4 J8rfMy2N+a0ekC4ls3FWou8ct2pFrzfCCG/hHSmLsJxwLEa8eDJodde+/QLepM43eSq3 BT7RxHFb6B8rR21iogIVMw3KIvy2K+lXoxiFnePxwHA+GQZcPMbuU8EDJZCzdhwnhFO8 nXyg== X-Gm-Message-State: ABy/qLaqVcKgRXWgrV6tT4f3IFeDzBQbr9JOmBfa0Eyl9UsL+/Qnexf8 BCg0tG20scFroqpav7sX1erzIZwh2Do= X-Google-Smtp-Source: APBJJlF95+kSFxBs9d4pDOtehohhALNf2zhk0CRH0P4ZIcPOxfGtYaIR5ilvDhFJ1p2u7OpKqjT4MbBf20Q= X-Received: from zagreus.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:5c37]) (user=seanjc job=sendgmr) by 2002:a25:8208:0:b0:cf2:9e82:a5b5 with SMTP id q8-20020a258208000000b00cf29e82a5b5mr18342ybk.8.1689970747834; Fri, 21 Jul 2023 13:19:07 -0700 (PDT) Reply-To: Sean Christopherson Date: Fri, 21 Jul 2023 13:18:42 -0700 In-Reply-To: <20230721201859.2307736-1-seanjc@google.com> Mime-Version: 1.0 References: <20230721201859.2307736-1-seanjc@google.com> X-Mailer: git-send-email 2.41.0.487.g6d72f3e995-goog Message-ID: <20230721201859.2307736-3-seanjc@google.com> Subject: [PATCH v4 02/19] x86/reboot: Harden virtualization hooks for emergency reboot From: Sean Christopherson To: Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, Sean Christopherson , Paolo Bonzini Cc: linux-kernel@vger.kernel.org, kvm@vger.kernel.org, Andrew Cooper , Kai Huang , Chao Gao Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Provide dedicated helpers to (un)register virt hooks used during an emergency crash/reboot, and WARN if there is an attempt to overwrite the registered callback, or an attempt to do an unpaired unregister. Opportunsitically use rcu_assign_pointer() instead of RCU_INIT_POINTER(), mainly so that the set/unset paths are more symmetrical, but also because any performance gains from using RCU_INIT_POINTER() are meaningless for this code. Reviewed-by: Kai Huang Signed-off-by: Sean Christopherson --- arch/x86/include/asm/reboot.h | 5 +++-- arch/x86/kernel/reboot.c | 30 ++++++++++++++++++++++++------ arch/x86/kvm/vmx/vmx.c | 6 ++---- 3 files changed, 29 insertions(+), 12 deletions(-) diff --git a/arch/x86/include/asm/reboot.h b/arch/x86/include/asm/reboot.h index dc201724a643..74c6a624d166 100644 --- a/arch/x86/include/asm/reboot.h +++ b/arch/x86/include/asm/reboot.h @@ -25,8 +25,9 @@ void __noreturn machine_real_restart(unsigned int type); #define MRR_BIOS 0 #define MRR_APM 1 =20 -typedef void crash_vmclear_fn(void); -extern crash_vmclear_fn __rcu *crash_vmclear_loaded_vmcss; +typedef void (cpu_emergency_virt_cb)(void); +void cpu_emergency_register_virt_callback(cpu_emergency_virt_cb *callback); +void cpu_emergency_unregister_virt_callback(cpu_emergency_virt_cb *callbac= k); void cpu_emergency_disable_virtualization(void); =20 typedef void (*nmi_shootdown_cb)(int, struct pt_regs*); diff --git a/arch/x86/kernel/reboot.c b/arch/x86/kernel/reboot.c index 3fa4c6717a1d..62ccedeb5e2b 100644 --- a/arch/x86/kernel/reboot.c +++ b/arch/x86/kernel/reboot.c @@ -794,17 +794,35 @@ void machine_crash_shutdown(struct pt_regs *regs) * * protected by rcu. */ -crash_vmclear_fn __rcu *crash_vmclear_loaded_vmcss; -EXPORT_SYMBOL_GPL(crash_vmclear_loaded_vmcss); +static cpu_emergency_virt_cb __rcu *cpu_emergency_virt_callback; + +void cpu_emergency_register_virt_callback(cpu_emergency_virt_cb *callback) +{ + if (WARN_ON_ONCE(rcu_access_pointer(cpu_emergency_virt_callback))) + return; + + rcu_assign_pointer(cpu_emergency_virt_callback, callback); +} +EXPORT_SYMBOL_GPL(cpu_emergency_register_virt_callback); + +void cpu_emergency_unregister_virt_callback(cpu_emergency_virt_cb *callbac= k) +{ + if (WARN_ON_ONCE(rcu_access_pointer(cpu_emergency_virt_callback) !=3D cal= lback)) + return; + + rcu_assign_pointer(cpu_emergency_virt_callback, NULL); + synchronize_rcu(); +} +EXPORT_SYMBOL_GPL(cpu_emergency_unregister_virt_callback); =20 static inline void cpu_crash_vmclear_loaded_vmcss(void) { - crash_vmclear_fn *do_vmclear_operation =3D NULL; + cpu_emergency_virt_cb *callback; =20 rcu_read_lock(); - do_vmclear_operation =3D rcu_dereference(crash_vmclear_loaded_vmcss); - if (do_vmclear_operation) - do_vmclear_operation(); + callback =3D rcu_dereference(cpu_emergency_virt_callback); + if (callback) + callback(); rcu_read_unlock(); } =20 diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c index 7f692d97a821..019cefc65142 100644 --- a/arch/x86/kvm/vmx/vmx.c +++ b/arch/x86/kvm/vmx/vmx.c @@ -8590,8 +8590,7 @@ static void __vmx_exit(void) { allow_smaller_maxphyaddr =3D false; =20 - RCU_INIT_POINTER(crash_vmclear_loaded_vmcss, NULL); - synchronize_rcu(); + cpu_emergency_unregister_virt_callback(crash_vmclear_local_loaded_vmcss); =20 vmx_cleanup_l1d_flush(); } @@ -8641,8 +8640,7 @@ static int __init vmx_init(void) pi_init_cpu(cpu); } =20 - rcu_assign_pointer(crash_vmclear_loaded_vmcss, - crash_vmclear_local_loaded_vmcss); + cpu_emergency_register_virt_callback(crash_vmclear_local_loaded_vmcss); =20 vmx_check_vmcs12_offsets(); =20 --=20 2.41.0.487.g6d72f3e995-goog