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 84761C433F5 for ; Mon, 28 Mar 2022 23:12:46 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230280AbiC1XO0 (ORCPT ); Mon, 28 Mar 2022 19:14:26 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:49684 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230240AbiC1XOY (ORCPT ); Mon, 28 Mar 2022 19:14:24 -0400 Received: from mail-ed1-x52c.google.com (mail-ed1-x52c.google.com [IPv6:2a00:1450:4864:20::52c]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 07F0F6447; Mon, 28 Mar 2022 16:12:43 -0700 (PDT) Received: by mail-ed1-x52c.google.com with SMTP id b24so18689019edu.10; Mon, 28 Mar 2022 16:12:42 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=nQG8j8adD47TTidkz+7AQDmn+QN52qQ6CCfa3YMx7v0=; b=PhxUbyL7+q0eHH7O68pKrAM5b8X839330NCsdzVny0YXgyTMH+wt8lFIB2OX8rDJWE jS9dUxvXCrcjGMnzIp8tY6VAvCfXGACQu1nb8NhkMe7WEhNTbViXrcZ+3Yh9FfWq73oO 0FibJiWDd5kh/ufBzC6ncxvwAVn4+Bocon6i8vcftHhVrUjYbwXvcFQeroPIook4n6oC io7EOcCvGQgBGl3gjYxE0vdSDIYNX9LPbe3w4xTzLXqJh7wXws/UfNQzKDxYEQyuP8YW FUTmCjkoCzQW8WkXrvP3vFMxpUIbwGI+F3kXHE3hg1qaYxFOvMJaEC/Q23L2N2M3+80r LICQ== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=nQG8j8adD47TTidkz+7AQDmn+QN52qQ6CCfa3YMx7v0=; b=eaCnfHZcywX/6MHDbLYH2h6hXNmHVfN1NCgFFUMOL0Xh+nwyRAJTRBFy3iwwPzXBjC oInKtsZ+K5rsgG3Ps6GKmIvtQw/FnQFHKrNlirXJbqmDLBL50KuuhOLrnZfHRdQ+GMVu egFfwS5lPuCnTwF7BKAhFcIRiQWL8mb+TDs9VQ40h9t0akLa1wetE6J4m5+ZZCSvFDJR ijApWDRpbdpsufv2rTzz9IzDl+s9W78KLcqaCf3aTVfzDsvO9iNj1rcH3ofO4KXqD+7S Z8AqVR4q+KE9+RKr+EJ3gQmbPX/bNGzhSht03DDlecm/RxjlquXIGmsBee8YwkfKGPcq O86g== X-Gm-Message-State: AOAM532VLEGjcJNl6Ztmu3Hh29V1ZbAvbLqSDykbbrLf7xKXArrK8dXe gHtoK2gY6U8dQDx9YnMAqBM= X-Google-Smtp-Source: ABdhPJxFSGw+5TZ5QabLOtItEkK1xbL5vSOfieJzZdVtUYlq6C/A6AugpQSUTsmNiMRAtbYS8k3k1A== X-Received: by 2002:a05:6402:43cc:b0:419:2486:6cd2 with SMTP id p12-20020a05640243cc00b0041924866cd2mr386960edc.334.1648509161391; Mon, 28 Mar 2022 16:12:41 -0700 (PDT) Received: from anparri (host-82-59-4-232.retail.telecomitalia.it. [82.59.4.232]) by smtp.gmail.com with ESMTPSA id v26-20020a50955a000000b00418ebdb07ddsm7746006eda.56.2022.03.28.16.12.40 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 28 Mar 2022 16:12:41 -0700 (PDT) Date: Tue, 29 Mar 2022 01:12:33 +0200 From: Andrea Parri To: Michael Kelley Cc: kys@microsoft.com, haiyangz@microsoft.com, sthemmin@microsoft.com, wei.liu@kernel.org, linux-kernel@vger.kernel.org, linux-hyperv@vger.kernel.org, vkuznets@redhat.com, decui@microsoft.com Subject: Re: [PATCH 1/1] hv: drivers: vmbus: Prevent load re-ordering when reading ring buffer Message-ID: <20220328231233.GA102571@anparri> References: <1648394710-33480-1-git-send-email-mikelley@microsoft.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1648394710-33480-1-git-send-email-mikelley@microsoft.com> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Sun, Mar 27, 2022 at 08:25:10AM -0700, Michael Kelley wrote: > When reading a packet from a host-to-guest ring buffer, there is no > memory barrier between reading the write index (to see if there is > a packet to read) and reading the contents of the packet. The Hyper-V > host uses store-release when updating the write index to ensure that > writes of the packet data are completed first. On the guest side, > the processor can reorder and read the packet data before the write > index, and sometimes get stale packet data. Getting such stale packet > data has been observed in a reproducible case in a VM on ARM64. > > Fix this by using virt_load_acquire() to read the write index, > ensuring that reads of the packet data cannot be reordered > before it. Preventing such reordering is logically correct, and > with this change, getting stale data can no longer be reproduced. > > Signed-off-by: Michael Kelley Reviewed-by: Andrea Parri (Microsoft) Nit: subject prefix -> "Drivers: hv: vmbus:". Thanks, Andrea