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=-19.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, USER_AGENT_GIT autolearn=unavailable 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 15DC3C4332F for ; Thu, 16 Sep 2021 17:29:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id EB86561139 for ; Thu, 16 Sep 2021 17:29:31 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1352992AbhIPR3h (ORCPT ); Thu, 16 Sep 2021 13:29:37 -0400 Received: from mail.kernel.org ([198.145.29.99]:44396 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1351994AbhIPRUK (ORCPT ); Thu, 16 Sep 2021 13:20:10 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id 9AB6B61BA3; Thu, 16 Sep 2021 16:42:05 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1631810526; bh=50YXhMmBJBhR55rbNXd7AEWdWQP1PFZ8gTBGr6jGd08=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=A4DfzvMCQZK+4o/XobWxP6DYZDlByYXbHchGmd3W61If22msZ55lsgdAbNta50oLy zXmKsMPw887RzgcJAAVoeybKyUSsqNjVeB1IcWvMYtetCqxEirXM+SCLmgImfKydBx Ae17UnsA75ovUAwk91BYuaggFrZc6Gio7JuLM/WE= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Ani Sinha , Michael Kelley , Wei Liu , Sasha Levin Subject: [PATCH 5.14 174/432] x86/hyperv: fix for unwanted manipulation of sched_clock when TSC marked unstable Date: Thu, 16 Sep 2021 17:58:43 +0200 Message-Id: <20210916155816.639918053@linuxfoundation.org> X-Mailer: git-send-email 2.33.0 In-Reply-To: <20210916155810.813340753@linuxfoundation.org> References: <20210916155810.813340753@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: linux-kernel@vger.kernel.org From: Ani Sinha [ Upstream commit c445535c3efbfb8cb42d098e624d46ab149664b7 ] Marking TSC as unstable has a side effect of marking sched_clock as unstable when TSC is still being used as the sched_clock. This is not desirable. Hyper-V ultimately uses a paravirtualized clock source that provides a stable scheduler clock even on systems without TscInvariant CPU capability. Hence, mark_tsc_unstable() call should be called _after_ scheduler clock has been changed to the paravirtualized clocksource. This will prevent any unwanted manipulation of the sched_clock. Only TSC will be correctly marked as unstable. Signed-off-by: Ani Sinha Reviewed-by: Michael Kelley Tested-by: Michael Kelley Link: https://lore.kernel.org/r/20210713030522.1714803-1-ani@anisinha.ca Signed-off-by: Wei Liu Signed-off-by: Sasha Levin --- arch/x86/kernel/cpu/mshyperv.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/cpu/mshyperv.c b/arch/x86/kernel/cpu/mshyperv.c index c890d67a64ad..ba54c44a64e2 100644 --- a/arch/x86/kernel/cpu/mshyperv.c +++ b/arch/x86/kernel/cpu/mshyperv.c @@ -375,8 +375,6 @@ static void __init ms_hyperv_init_platform(void) if (ms_hyperv.features & HV_ACCESS_TSC_INVARIANT) { wrmsrl(HV_X64_MSR_TSC_INVARIANT_CONTROL, 0x1); setup_force_cpu_cap(X86_FEATURE_TSC_RELIABLE); - } else { - mark_tsc_unstable("running on Hyper-V"); } /* @@ -437,6 +435,13 @@ static void __init ms_hyperv_init_platform(void) /* Register Hyper-V specific clocksource */ hv_init_clocksource(); #endif + /* + * TSC should be marked as unstable only after Hyper-V + * clocksource has been initialized. This ensures that the + * stability of the sched_clock is not altered. + */ + if (!(ms_hyperv.features & HV_ACCESS_TSC_INVARIANT)) + mark_tsc_unstable("running on Hyper-V"); } static bool __init ms_hyperv_x2apic_available(void) -- 2.30.2