From mboxrd@z Thu Jan 1 00:00:00 1970 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 5945CC43219 for ; Tue, 25 Jan 2022 00:08:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2369617AbiAYACP (ORCPT ); Mon, 24 Jan 2022 19:02:15 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:53428 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1458155AbiAXX2Q (ORCPT ); Mon, 24 Jan 2022 18:28:16 -0500 Received: from ams.source.kernel.org (ams.source.kernel.org [IPv6:2604:1380:4601:e00::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 0B1E8C0A54D4; Mon, 24 Jan 2022 13:32:48 -0800 (PST) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by ams.source.kernel.org (Postfix) with ESMTPS id C8343B80FA1; Mon, 24 Jan 2022 21:32:46 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 01633C340E4; Mon, 24 Jan 2022 21:32:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1643059965; bh=tedjfVLlqp5z8Y5ric/qPSjsl1AyBDAz7qNYDDiK5L4=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=nk6hIkux0JOWPWMJ21SReA0vynFTuCVd7KqCw06+IidMnJK6RngqgFf/DmCk0IqUD Ah+re0Rc5T4/3NotpGnZCSWLRr9GreEHWY4wsIuarW7g7HwPyPzfeKmqhsEomnrOjG t6NOrFbBqez8Sc5fOdOkWTL0aV07VJmceuafoUF0= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Hou Wenlong , Paolo Bonzini , Sasha Levin Subject: [PATCH 5.16 0793/1039] KVM: x86: Exit to userspace if emulation prepared a completion callback Date: Mon, 24 Jan 2022 19:43:02 +0100 Message-Id: <20220124184151.954250852@linuxfoundation.org> X-Mailer: git-send-email 2.34.1 In-Reply-To: <20220124184125.121143506@linuxfoundation.org> References: <20220124184125.121143506@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org From: Hou Wenlong [ Upstream commit adbfb12d4c4517a8adde23a7fc46538953d56eea ] em_rdmsr() and em_wrmsr() return X86EMUL_IO_NEEDED if MSR accesses required an exit to userspace. However, x86_emulate_insn() doesn't return X86EMUL_*, so x86_emulate_instruction() doesn't directly act on X86EMUL_IO_NEEDED; instead, it looks for other signals to differentiate between PIO, MMIO, etc. causing RDMSR/WRMSR emulation not to exit to userspace now. Nevertheless, if the userspace_msr_exit_test testcase in selftests is changed to test RDMSR/WRMSR with a forced emulation prefix, the test passes. What happens is that first userspace exit information is filled but the userspace exit does not happen. Because x86_emulate_instruction() returns 1, the guest retries the instruction---but this time RIP has already been adjusted past the forced emulation prefix, so the guest executes RDMSR/WRMSR and the userspace exit finally happens. Since the X86EMUL_IO_NEEDED path has provided a complete_userspace_io callback, x86_emulate_instruction() can just return 0 if the callback is not NULL. Then RDMSR/WRMSR instruction emulation will exit to userspace directly, without the RDMSR/WRMSR vmexit. Fixes: 1ae099540e8c7 ("KVM: x86: Allow deflecting unknown MSR accesses to user space") Signed-off-by: Hou Wenlong Signed-off-by: Paolo Bonzini Message-Id: <56f9df2ee5c05a81155e2be366c9dc1f7adc8817.1635842679.git.houwenlong93@linux.alibaba.com> Signed-off-by: Sasha Levin --- 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 5d5a8e75edcb7..00628031de98d 100644 --- a/arch/x86/kvm/x86.c +++ b/arch/x86/kvm/x86.c @@ -8203,6 +8203,9 @@ restart: writeback = false; r = 0; vcpu->arch.complete_userspace_io = complete_emulated_mmio; + } else if (vcpu->arch.complete_userspace_io) { + writeback = false; + r = 0; } else if (r == EMULATION_RESTART) goto restart; else -- 2.34.1