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 X-Spam-Level: X-Spam-Status: No, score=-6.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id C78B4C4360C for ; Tue, 8 Oct 2019 18:08:13 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id AAC8921721 for ; Tue, 8 Oct 2019 18:08:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729815AbfJHSIM (ORCPT ); Tue, 8 Oct 2019 14:08:12 -0400 Received: from mx1.redhat.com ([209.132.183.28]:41808 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726138AbfJHSIM (ORCPT ); Tue, 8 Oct 2019 14:08:12 -0400 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.phx2.redhat.com [10.5.11.12]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 064547BDD2; Tue, 8 Oct 2019 18:08:12 +0000 (UTC) Received: from vitty.brq.redhat.com (ovpn-204-35.brq.redhat.com [10.40.204.35]) by smtp.corp.redhat.com (Postfix) with ESMTP id 24EBD60BE0; Tue, 8 Oct 2019 18:08:09 +0000 (UTC) From: Vitaly Kuznetsov To: kvm@vger.kernel.org Cc: linux-kernel@vger.kernel.org, Paolo Bonzini , Sean Christopherson , Jim Mattson Subject: [PATCH] selftests: kvm: fix sync_regs_test with newer gccs Date: Tue, 8 Oct 2019 20:08:08 +0200 Message-Id: <20191008180808.14181-1-vkuznets@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.26]); Tue, 08 Oct 2019 18:08:12 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit 204c91eff798a ("KVM: selftests: do not blindly clobber registers in guest asm") was intended to make test more gcc-proof, however, the result is exactly the opposite: on newer gccs (e.g. 8.2.1) the test breaks with ==== Test Assertion Failure ==== x86_64/sync_regs_test.c:168: run->s.regs.regs.rbx == 0xBAD1DEA + 1 pid=14170 tid=14170 - Invalid argument 1 0x00000000004015b3: main at sync_regs_test.c:166 (discriminator 6) 2 0x00007f413fb66412: ?? ??:0 3 0x000000000040191d: _start at ??:? rbx sync regs value incorrect 0x1. Apparently, compile is still free to play games with registers even when they have variables attaches. Re-write guest code with 'asm volatile' by embedding ucall there and making sure rbx is preserved. Fixes: 204c91eff798a ("KVM: selftests: do not blindly clobber registers in guest asm") Signed-off-by: Vitaly Kuznetsov --- .../selftests/kvm/x86_64/sync_regs_test.c | 21 ++++++++++--------- 1 file changed, 11 insertions(+), 10 deletions(-) diff --git a/tools/testing/selftests/kvm/x86_64/sync_regs_test.c b/tools/testing/selftests/kvm/x86_64/sync_regs_test.c index 11c2a70a7b87..5c8224256294 100644 --- a/tools/testing/selftests/kvm/x86_64/sync_regs_test.c +++ b/tools/testing/selftests/kvm/x86_64/sync_regs_test.c @@ -22,18 +22,19 @@ #define VCPU_ID 5 +#define UCALL_PIO_PORT ((uint16_t)0x1000) + +/* + * ucall is embedded here to protect against compiler reshuffling registers + * before calling a function. In this test we only need to get KVM_EXIT_IO + * vmexit and preserve RBX, no additional information is needed. + */ void guest_code(void) { - /* - * use a callee-save register, otherwise the compiler - * saves it around the call to GUEST_SYNC. - */ - register u32 stage asm("rbx"); - for (;;) { - GUEST_SYNC(0); - stage++; - asm volatile ("" : : "r" (stage)); - } + asm volatile("1: in %[port], %%al\n" + "add $0x1, %%rbx\n" + "jmp 1b" + : : [port] "d" (UCALL_PIO_PORT) : "rax", "rbx"); } static void compare_regs(struct kvm_regs *left, struct kvm_regs *right) -- 2.20.1