From nobody Thu Apr 9 06:20:25 2026 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 BF6A1C4332F for ; Wed, 2 Nov 2022 20:54:08 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231422AbiKBUyH (ORCPT ); Wed, 2 Nov 2022 16:54:07 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43900 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231377AbiKBUyD (ORCPT ); Wed, 2 Nov 2022 16:54:03 -0400 Received: from mail-pl1-x649.google.com (mail-pl1-x649.google.com [IPv6:2607:f8b0:4864:20::649]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7068D65E9 for ; Wed, 2 Nov 2022 13:54:03 -0700 (PDT) Received: by mail-pl1-x649.google.com with SMTP id i17-20020a170902cf1100b00183e2a963f5so11939plg.5 for ; Wed, 02 Nov 2022 13:54:03 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=google.com; s=20210112; h=cc:to:from:subject:message-id:mime-version:date:from:to:cc:subject :date:message-id:reply-to; bh=DP6Vz9iL0RlSaCYvirKZYjgQfbvTBUMyha6I3zFcOmY=; b=QjwaCGvbGka7XMhNLDn7aFQL0++Yn0EPdP+DSYDpcpQPhmenMWMLg5xAKRmvRdxAOK dAV/JiQeg2q4NVVKpyHV09iJWusW6WxdOi0a2+ffSQ9hSc1iDIFtqKO1ruBPYlurFZ+g 7rMp3uQxtpHPndcgMXIEiKM5oAeKWlpjbKapbsu3aUvheZM5LibJpTjzSz8k2d2VITWp NLcslt1f3UNLNkd3BzHVvvA73QW+1rPQcqSFnGUbp9MPfMJXQJU6sSb7rgyrT0rngoBJ HAkzzZJOqIvjCXjA2stygmj5L5niYvyoXPl8KGTWKcfW0hfCuUuBHGPJaOdiZD80H7zH Y3jg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=cc:to:from:subject:message-id:mime-version:date:x-gm-message-state :from:to:cc:subject:date:message-id:reply-to; bh=DP6Vz9iL0RlSaCYvirKZYjgQfbvTBUMyha6I3zFcOmY=; b=xZE7BTZFrt2uu/dBDkttzYE4Bd26zh3OH05+U45r6DujZJ8BwCvX94kxCXfyXkp3S1 Sp/N+GY5UeqOCO5aRMc39NsqS6MQZ1MSpU/9iSU3+QFdrWVA97oI/UtLeIFcposugTPB tpuKfxjVwreXt7vRuu7vV8OdIS1+x5Rfj7gRYiq4WRJ44NBkpRxsTJo2IrYhp42vDCbq hQcfivgCWKGsLIxnim1w8FlWpzRmuTX7buA0dk7+17erd1mR48iUPHqY/nGstcM4heYA y6u9Vi3mssQSR8p2Cq0715PvqIzELB62Af0TSx312x4EpGDvNX6oTrOjRhvzqQSp3ysa /ewg== X-Gm-Message-State: ACrzQf21Rn9Ow9BAFQgFJ0O8q3L26m1eYMINceD6KRzPcQpDqKoaiXtL mp9CfTqVyMfOQTH+Ee3Qup9YTIOP+xBJ1HEnzk0pq4fX2WJt93rvwnTWrHv2ifcBoE//39zOUFB 3nlM1FitHNXwBFyfF4NaDwsMcbJN4qURDfOK5ij3FvccdERm63fh+ePJfXQgyx9MLzhPixJF9 X-Google-Smtp-Source: AMsMyM7Ob4hJ10H8x0X5FE8OSoFlNs6vFoc5b7/Y6ocniDFi5W6BAzjyOycoyJB24joAcsjEIwsW21krNTZN X-Received: from sweer.c.googlers.com ([fda3:e722:ac3:cc00:7f:e700:c0a8:e45]) (user=bgardon job=sendgmr) by 2002:a05:6a00:1d06:b0:56b:ec38:27e9 with SMTP id a6-20020a056a001d0600b0056bec3827e9mr26575631pfx.71.1667422442741; Wed, 02 Nov 2022 13:54:02 -0700 (PDT) Date: Wed, 2 Nov 2022 20:53:59 +0000 Mime-Version: 1.0 X-Mailer: git-send-email 2.38.1.431.g37b22c650d-goog Message-ID: <20221102205359.1260980-1-bgardon@google.com> Subject: [PATCH v2] KVM: x86: Use SRCU to protect zap in __kvm_set_or_clear_apicv_inhibit() From: Ben Gardon To: linux-kernel@vger.kernel.org, kvm@vger.kernel.org Cc: Paolo Bonzini , Sean Christopherson , David Matlack , Anish Ghulati , Ben Gardon , Greg Thelen Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" kvm_zap_gfn_range() must be called in an SRCU read-critical section, but there is no SRCU annotation in __kvm_set_or_clear_apicv_inhibit(). This can lead to the following warning via kvm_arch_vcpu_ioctl_set_guest_debug() if a Shadow MMU is in use (TDP MMU disabled or nesting): [ 1416.659809] =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D [ 1416.659810] WARNING: suspicious RCU usage [ 1416.659839] 6.1.0-dbg-DEV #1 Tainted: G S I [ 1416.659853] ----------------------------- [ 1416.659854] include/linux/kvm_host.h:954 suspicious rcu_dereference_chec= k() usage! [ 1416.659856] ... [ 1416.659904] dump_stack_lvl+0x84/0xaa [ 1416.659910] dump_stack+0x10/0x15 [ 1416.659913] lockdep_rcu_suspicious+0x11e/0x130 [ 1416.659919] kvm_zap_gfn_range+0x226/0x5e0 [ 1416.659926] ? kvm_make_all_cpus_request_except+0x18b/0x1e0 [ 1416.659935] __kvm_set_or_clear_apicv_inhibit+0xcc/0x100 [ 1416.659940] kvm_arch_vcpu_ioctl_set_guest_debug+0x350/0x390 [ 1416.659946] kvm_vcpu_ioctl+0x2fc/0x620 [ 1416.659955] __se_sys_ioctl+0x77/0xc0 [ 1416.659962] __x64_sys_ioctl+0x1d/0x20 [ 1416.659965] do_syscall_64+0x3d/0x80 [ 1416.659969] entry_SYSCALL_64_after_hwframe+0x63/0xcd Always take the KVM SRCU read lock in __kvm_set_or_clear_apicv_inhibit() to protect the GFN to memslot translation. The SRCU read lock is not technically required when no Shadow MMUs are in use, since the TDP MMU walks the paging structures from the roots and does not need to look up GFN translations in the memslots, but make the SRCU locking unconditional for simplicty. In most cases, the SRCU locking is taken care of in the vCPU run loop, but when called through the KVM_SET_GUEST_DEBUG IOCTL, the SRCU read lock is missing. Tested: ran tools/testing/selftests/kvm/x86_64/debug_regs on a DBG build. This patch causes the suspicious RCU warning to disappear. Note that the warning is hit in __kvm_zap_rmaps(), so kvm_memslots_have_rmaps() must return true in order for this to repro (i.e. the TDP MMU must be off or nesting in use.) Reported-by: Greg Thelen Fixes: 36222b117e36 ("KVM: x86: don't disable APICv memslot when inhibited") Signed-off-by: Ben Gardon Reviewed-by: Sean Christopherson --- arch/x86/kvm/x86.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index cd9eb13e2ed7..6d853e5f683d 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -10091,7 +10091,10 @@ void __kvm_set_or_clear_apicv_inhibit(struct kvm *= kvm, kvm->arch.apicv_inhibit_reasons =3D new; if (new) { unsigned long gfn =3D gpa_to_gfn(APIC_DEFAULT_PHYS_BASE); + int idx =3D srcu_read_lock(&kvm->srcu); + kvm_zap_gfn_range(kvm, gfn, gfn+1); + srcu_read_unlock(&kvm->srcu, idx); } } else { kvm->arch.apicv_inhibit_reasons =3D new; --=20 2.38.1.431.g37b22c650d-goog