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 89B4DC433F5 for ; Mon, 30 May 2022 14:48:57 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238812AbiE3OsN (ORCPT ); Mon, 30 May 2022 10:48:13 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34634 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241624AbiE3O0U (ORCPT ); Mon, 30 May 2022 10:26:20 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D0BA3AF1E5; Mon, 30 May 2022 06:51:12 -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 B1B7B60F22; Mon, 30 May 2022 13:51:12 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 136CAC385B8; Mon, 30 May 2022 13:51:10 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1653918672; bh=L4wMv7eVCEcb+Dh8ypbivhOGsg3GXEYdwwoPqDs6iew=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=M0sfjiro7hWkYkV/KY1qKm/by3EchkrAwTdEU7iyJ1LPi/ZRqW1onH/1Aru7jX5jc cVq5rDqoS7JGUEaUz7oYivSJK9H0kH4sIVkA2y+xgjzP/M2R5Sc0PQgcvJOzUCr1tl W9bbHf4PqNJw35FpiB0t9vd+lLl48Ijxbmz/Den0U4S7R9JIJhNux+c0FEN1dxZlV/ YGHdeJHKI9/mC5NYGuiO9dhkIr/oTNKGhIqxn7koOxADpnOyCwGo+cLDrRQn6IGZ+D v8LoXsrqqsP94Xx9hKF3CCG0AFZLE5lR09YmRa5uw8b3T1zx5yQiFXdtKIhw7lkBwr 9+BcuygNY/ctQ== 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 4.14 06/29] ACPICA: Avoid cache flush inside virtual machines Date: Mon, 30 May 2022 09:50:33 -0400 Message-Id: <20220530135057.1937286-6-sashal@kernel.org> X-Mailer: git-send-email 2.35.1 In-Reply-To: <20220530135057.1937286-1-sashal@kernel.org> References: <20220530135057.1937286-1-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