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 D1DEAC433EF for ; Thu, 30 Jun 2022 11:34:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S234249AbiF3LeK (ORCPT ); Thu, 30 Jun 2022 07:34:10 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50490 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S234133AbiF3LeJ (ORCPT ); Thu, 30 Jun 2022 07:34:09 -0400 Received: from ams.source.kernel.org (ams.source.kernel.org [145.40.68.75]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BB5445A445 for ; Thu, 30 Jun 2022 04:34:07 -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 ams.source.kernel.org (Postfix) with ESMTPS id 5C4EDB82A39 for ; Thu, 30 Jun 2022 11:34:06 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id B8395C34115; Thu, 30 Jun 2022 11:34:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1656588845; bh=y/AkczZu+t5L5QS5HmrGxEEOZZGTi1cFRhvgGwdbbLY=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Qmg64MZn4FHh18uQWV6rRCe66knAFc1oY1fGEQzGn712mLfl0ROVycbbNXMHzHvRE MFxzjNM4zEBjQ1LYcJ27YupCdzXULyW26LOoR+89hp0WyuqCpZtxlSb8ZEvpERkHOS p5wIiaR8x/xOeSlz1dkr3si+QRXTeavd7RI3LzlE= Date: Thu, 30 Jun 2022 13:34:02 +0200 From: Greg KH To: Demi Marie Obenour Cc: stable@vger.kernel.org, Xen developer discussion , Juergen Gross Subject: Re: [PATCH 5.10] xen/gntdev: Avoid blocking in unmap_grant_pages() Message-ID: References: <20220627181006.1954-1-demi@invisiblethingslab.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220627181006.1954-1-demi@invisiblethingslab.com> Precedence: bulk List-ID: X-Mailing-List: stable@vger.kernel.org On Mon, Jun 27, 2022 at 02:10:02PM -0400, Demi Marie Obenour wrote: > commit dbe97cff7dd9f0f75c524afdd55ad46be3d15295 upstream > > unmap_grant_pages() currently waits for the pages to no longer be used. > In https://github.com/QubesOS/qubes-issues/issues/7481, this lead to a > deadlock against i915: i915 was waiting for gntdev's MMU notifier to > finish, while gntdev was waiting for i915 to free its pages. I also > believe this is responsible for various deadlocks I have experienced in > the past. > > Avoid these problems by making unmap_grant_pages async. This requires > making it return void, as any errors will not be available when the > function returns. Fortunately, the only use of the return value is a > WARN_ON(), which can be replaced by a WARN_ON when the error is > detected. Additionally, a failed call will not prevent further calls > from being made, but this is harmless. > > Because unmap_grant_pages is now async, the grant handle will be sent to > INVALID_GRANT_HANDLE too late to prevent multiple unmaps of the same > handle. Instead, a separate bool array is allocated for this purpose. > This wastes memory, but stuffing this information in padding bytes is > too fragile. Furthermore, it is necessary to grab a reference to the > map before making the asynchronous call, and release the reference when > the call returns. > > It is also necessary to guard against reentrancy in gntdev_map_put(), > and to handle the case where userspace tries to map a mapping whose > contents have not all been freed yet. > > Fixes: 745282256c75 ("xen/gntdev: safely unmap grants in case they are still in use") > Cc: stable@vger.kernel.org > Signed-off-by: Demi Marie Obenour > Reviewed-by: Juergen Gross > Link: https://lore.kernel.org/r/20220622022726.2538-1-demi@invisiblethingslab.com > Signed-off-by: Juergen Gross > --- > drivers/xen/gntdev-common.h | 7 ++ > drivers/xen/gntdev.c | 142 +++++++++++++++++++++++++----------- > 2 files changed, 106 insertions(+), 43 deletions(-) All now queued up, thanks. greg k-h