From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 375442741A0; Mon, 23 Mar 2026 14:53:06 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774277586; cv=none; b=cUssEWmOgrRJaVY99kOszhrnBHMRLuxlMzYeZGjlS+1Rf+NfwOVWDada3E8MfYqUk1DpVndjBFM9gXPINeUpNlmVrGIvePsQKqkAb/6zr7zUjQ6nS+OBdDdn+2jNqQIkO1UwtFrUkFrQ61uv2bcH5bqrwGQAM1RmcyIGWKGYa64= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774277586; c=relaxed/simple; bh=9bCfTXRT9xHqGeJYUGJLC4ppxn/ELbNNp7c4algXYZc=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=qE9oScjA49ZhuTzNJzFiPRshYCrm9IJ1KNTMQMgih4SdHePiGAKuEgeQkOus22xIcrAdfSZYNrj50XjFttggybxcgEFNWnOXqds5RBLiafwd2pz4EMr9ZTmBuS0Etk1MKdzj086Ngqr1coIQu1uR9ODhfEkOxQYf20zEQcT3cqA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=RgCaCWl7; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b="RgCaCWl7" Received: by smtp.kernel.org (Postfix) with ESMTPSA id B0989C4CEF7; Mon, 23 Mar 2026 14:53:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1774277586; bh=9bCfTXRT9xHqGeJYUGJLC4ppxn/ELbNNp7c4algXYZc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=RgCaCWl7en3T+eUrwofcJRgOwxpRADXUXcBrRhREuslmO2gJ1293gpannl5pdG1WT 6IwSk2UhJRtpRqoWn36Qg1fAoxDFAVVU4yY1/6o0+UkD2RWaobLFH25ebEIA08QOsT 2/2epvFI7Tf8g16ZzRCP+YtrBgL6X0+DJVhaf0Pc= From: Greg Kroah-Hartman To: stable@vger.kernel.org Cc: Greg Kroah-Hartman , patches@lists.linux.dev, Alessandro Ratti , syzbot+1522459a74d26b0ac33a@syzkaller.appspotmail.com, Sean Christopherson , Sasha Levin Subject: [PATCH 6.6 040/567] KVM: x86: Ignore -EBUSY when checking nested events from vcpu_block() Date: Mon, 23 Mar 2026 14:39:20 +0100 Message-ID: <20260323134534.785615917@linuxfoundation.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260323134533.749096647@linuxfoundation.org> References: <20260323134533.749096647@linuxfoundation.org> User-Agent: quilt/0.69 X-stable: review X-Patchwork-Hint: ignore Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 6.6-stable review patch. If anyone has any objections, please let me know. ------------------ From: Sean Christopherson [ Upstream commit ead63640d4e72e6f6d464f4e31f7fecb79af8869 ] Ignore -EBUSY when checking nested events after exiting a blocking state while L2 is active, as exiting to userspace will generate a spurious userspace exit, usually with KVM_EXIT_UNKNOWN, and likely lead to the VM's demise. Continuing with the wakeup isn't perfect either, as *something* has gone sideways if a vCPU is awakened in L2 with an injected event (or worse, a nested run pending), but continuing on gives the VM a decent chance of surviving without any major side effects. As explained in the Fixes commits, it _should_ be impossible for a vCPU to be put into a blocking state with an already-injected event (exception, IRQ, or NMI). Unfortunately, userspace can stuff MP_STATE and/or injected events, and thus put the vCPU into what should be an impossible state. Don't bother trying to preserve the WARN, e.g. with an anti-syzkaller Kconfig, as WARNs can (hopefully) be added in paths where _KVM_ would be violating x86 architecture, e.g. by WARNing if KVM attempts to inject an exception or interrupt while the vCPU isn't running. Cc: Alessandro Ratti Cc: stable@vger.kernel.org Fixes: 26844fee6ade ("KVM: x86: never write to memory from kvm_vcpu_check_block()") Fixes: 45405155d876 ("KVM: x86: WARN if a vCPU gets a valid wakeup that KVM can't yet inject") Link: https://syzkaller.appspot.com/text?tag=ReproC&x=10d4261a580000 Reported-by: syzbot+1522459a74d26b0ac33a@syzkaller.appspotmail.com Closes: https://lore.kernel.org/all/671bc7a7.050a0220.455e8.022a.GAE@google.com Link: https://patch.msgid.link/20260109030657.994759-1-seanjc@google.com Signed-off-by: Sean Christopherson Signed-off-by: Sasha Levin --- arch/x86/kvm/x86.c | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c index 3edfcb4090b18..ac0b458582c38 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -11005,8 +11005,7 @@ static inline int vcpu_block(struct kvm_vcpu *vcpu) if (is_guest_mode(vcpu)) { int r = kvm_check_nested_events(vcpu); - WARN_ON_ONCE(r == -EBUSY); - if (r < 0) + if (r < 0 && r != -EBUSY) return 0; } -- 2.51.0