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 A68E526F288; Thu, 12 Mar 2026 20:17:09 +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=1773346629; cv=none; b=LGOU2Q+2bozNtItRnnvcqUSFfibDC87vKtQh0Am8vmUKAmoXUQnzXphQoYwpWhfzxu9m3cpDu+zdpaZF7h5JFU/gMF4/q/7MJH13fkFMjrrY+eSadSMo2IpBP+0zmBtcEKJSv0yUS+sjBXrN9Bo7g0eYTjHiF+HWCJ/I+6k0bUs= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1773346629; c=relaxed/simple; bh=B460u3FW2gszZwUYXoJP/+AoTHH2CFQr4/97kZIPZZc=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=EMgodgEekG0zhAUJLO0lHOPRWQiQ+62SWFXV99WSvGfEG01y1rR8L1pHs0Bj0v6rIoJv4Tqw6oejnTUAzGzrEUNd6b//C15F1yCUoTW5B4c386d7H6Wu+J3CVE4bytmYXLIn4EiIeKsvLEDsTVGIzK7SJ9QJX5iFOGd7DQ0SD9U= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=linuxfoundation.org header.i=@linuxfoundation.org header.b=i6+UWl4a; 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="i6+UWl4a" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 71958C4CEF7; Thu, 12 Mar 2026 20:17:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1773346629; bh=B460u3FW2gszZwUYXoJP/+AoTHH2CFQr4/97kZIPZZc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=i6+UWl4amx6OqG82MmRghI21YkH2I+/awyn//9kh24w+zbA0l1dsbmHLLgCyaOOyB Oe1kOw5b4jsXE7ZlKNu1r7bu6G7M3alJYERL06D/E3scb9c2JOsBJ8Jp+z+ZIggQ2L 0Je2UGGfdRLYPC5/Aa5x36RazF5MJuKkxkxyW1jE= 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 6.12 054/265] KVM: x86: Ignore -EBUSY when checking nested events from vcpu_block() Date: Thu, 12 Mar 2026 21:07:21 +0100 Message-ID: <20260312201020.161040398@linuxfoundation.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260312201018.128816016@linuxfoundation.org> References: <20260312201018.128816016@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 6.12-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 8f673aaa0490f..0d9035993ed36 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -11285,8 +11285,7 @@ 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