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=-2.4 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 122A5C433DF for ; Sat, 16 May 2020 06:54:37 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DDA4720825 for ; Sat, 16 May 2020 06:54:36 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (1024-bit key) header.d=alien8.de header.i=@alien8.de header.b="VHURHVKx" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726801AbgEPGyg (ORCPT ); Sat, 16 May 2020 02:54:36 -0400 Received: from mail.skyhub.de ([5.9.137.197]:57376 "EHLO mail.skyhub.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725275AbgEPGyf (ORCPT ); Sat, 16 May 2020 02:54:35 -0400 Received: from zn.tnic (p200300EC2F1DA50090D29301FFFB4BAE.dip0.t-ipconnect.de [IPv6:2003:ec:2f1d:a500:90d2:9301:fffb:4bae]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.skyhub.de (SuperMail on ZX Spectrum 128k) with ESMTPSA id 9B50B1EC01AD; Sat, 16 May 2020 08:54:34 +0200 (CEST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=alien8.de; s=dkim; t=1589612074; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:in-reply-to:in-reply-to: references:references; bh=ab+P+wPx5NHYsiPgc9J2JsoTDiY7IzZ3zmWeot+Qw+U=; b=VHURHVKx6gfcC8pR4Uqeylj3W7FJdMBA5fjAMqIYMpipQmPnLRkxCuYO9pW2i5KsG68avv B7jWGHGb1O48AIbsWOmy7pxZuc5CoZccvFfhfHVX3ltEWmgjF3vWwt8bahV1me9SoUCMnq i89iEUt/tBdq1xyqWHkkmphz7XlRpEk= Date: Sat, 16 May 2020 08:54:31 +0200 From: Borislav Petkov To: Tony Luck Cc: Jue Wang , Dan Williams , x86@kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] x86/mm: Don't try to change poison pages to uncacheable in a guest Message-ID: <20200516065431.GB25771@zn.tnic> References: <20200505184648.2264-1-tony.luck@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: <20200505184648.2264-1-tony.luck@intel.com> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, May 05, 2020 at 11:46:48AM -0700, Tony Luck wrote: > An interesting thing happened when a guest Linux instance took > a machine check. The VMM unmapped the bad page from guest physical > space and passed the machine check to the guest. > > Linux took all the normal actions to offline the page from the process > that was using it. But then guest Linux crashed because it said there > was a second machine check inside the kernel with this stack trace: > > do_memory_failure > set_mce_nospec > set_memory_uc > _set_memory_uc > change_page_attr_set_clr > cpa_flush > clflush_cache_range_opt Maybe I don't see it but how can clflush_cache_range_opt() call cpa_flush() ? > This was odd, because a CLFLUSH instruction shouldn't raise a machine > check (it isn't consuming the data). Further investigation showed that > the VMM had passed in another machine check because is appeared that the > guest was accessing the bad page. This is where you lost me - if the VMM unmaps the page during the first MCE, how can the guest even attempt to touch it and do this stack trace above? /me is confused. -- Regards/Gruss, Boris. https://people.kernel.org/tglx/notes-about-netiquette