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 BB268C4332F for ; Mon, 30 May 2022 14:51:38 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S241839AbiE3Ouh (ORCPT ); Mon, 30 May 2022 10:50:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42586 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241887AbiE3Oaj (ORCPT ); Mon, 30 May 2022 10:30:39 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [139.178.84.217]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 922307CDE5; Mon, 30 May 2022 06:52:29 -0700 (PDT) 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 dfw.source.kernel.org (Postfix) with ESMTPS id 9247760FD4; Mon, 30 May 2022 13:52:27 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id EB70CC3411A; Mon, 30 May 2022 13:52:25 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1653918747; bh=L4wMv7eVCEcb+Dh8ypbivhOGsg3GXEYdwwoPqDs6iew=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=lNKvnAJmrVcP3FDQXXUeRg6rkRHMqE2SK1uNc5TLZbAq1Aq6MFwSTVoBwSRCCwmXO AYTIalWDYfo/0tcyqQjbLqGaIMeiNzHNpA3tcbCaZEMzjxr91Gqhy2X5XF/6bsG/t5 Usgaf+lddDfnathhAzimCt0GYeKKNJvZFHWntDldr1z84z1yrHU/YJUuPX3znYuE3y 3/iHgVBwuumSiNk0FpvyMZ6hX618uU33zmzkHsDGCbWHuiIKJTvoebBacv+Zkb1fvA wDp0alwOyANEB7xSG5AwOiYh4WF2+fRUN9VihDrkKjUd83sBktHyKTzCxA+ll2tbKu BHUUzIFLzjeqg== From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: "Kirill A. Shutemov" , Dave Hansen , Dan Williams , Thomas Gleixner , Sasha Levin , mingo@redhat.com, bp@alien8.de, x86@kernel.org Subject: [PATCH AUTOSEL 4.9 06/24] ACPICA: Avoid cache flush inside virtual machines Date: Mon, 30 May 2022 09:51:53 -0400 Message-Id: <20220530135211.1937674-6-sashal@kernel.org> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20220530135211.1937674-1-sashal@kernel.org> References: <20220530135211.1937674-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: "Kirill A. Shutemov" [ Upstream commit e2efb6359e620521d1e13f69b2257de8ceaa9475 ] While running inside virtual machine, the kernel can bypass cache flushing. Changing sleep state in a virtual machine doesn't affect the host system sleep state and cannot lead to data loss. Before entering sleep states, the ACPI code flushes caches to prevent data loss using the WBINVD instruction. This mechanism is required on bare metal. But, any use WBINVD inside of a guest is worthless. Changing sleep state in a virtual machine doesn't affect the host system sleep state and cannot lead to data loss, so most hypervisors simply ignore it. Despite this, the ACPI code calls WBINVD unconditionally anyway. It's useless, but also normally harmless. In TDX guests, though, WBINVD stops being harmless; it triggers a virtualization exception (#VE). If the ACPI cache-flushing WBINVD were left in place, TDX guests would need handling to recover from the exception. Avoid using WBINVD whenever running under a hypervisor. This both removes the useless WBINVDs and saves TDX from implementing WBINVD handling. Signed-off-by: Kirill A. Shutemov Signed-off-by: Dave Hansen Reviewed-by: Dave Hansen Reviewed-by: Dan Williams Reviewed-by: Thomas Gleixner Link: https://lkml.kernel.org/r/20220405232939.73860-30-kirill.shutemov@linux.intel.com Signed-off-by: Sasha Levin --- arch/x86/include/asm/acenv.h | 14 +++++++++++++- 1 file changed, 13 insertions(+), 1 deletion(-) diff --git a/arch/x86/include/asm/acenv.h b/arch/x86/include/asm/acenv.h index 1b010a859b8b..6de59a4f723c 100644 --- a/arch/x86/include/asm/acenv.h +++ b/arch/x86/include/asm/acenv.h @@ -16,7 +16,19 @@ /* Asm macros */ -#define ACPI_FLUSH_CPU_CACHE() wbinvd() +/* + * ACPI_FLUSH_CPU_CACHE() flushes caches on entering sleep states. + * It is required to prevent data loss. + * + * While running inside virtual machine, the kernel can bypass cache flushing. + * Changing sleep state in a virtual machine doesn't affect the host system + * sleep state and cannot lead to data loss. + */ +#define ACPI_FLUSH_CPU_CACHE() \ +do { \ + if (!cpu_feature_enabled(X86_FEATURE_HYPERVISOR)) \ + wbinvd(); \ +} while (0) int __acpi_acquire_global_lock(unsigned int *lock); int __acpi_release_global_lock(unsigned int *lock); -- 2.35.1