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=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS autolearn=ham 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 DA513C06510 for ; Tue, 2 Jul 2019 09:51:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id BAA9B206A2 for ; Tue, 2 Jul 2019 09:51:45 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727188AbfGBJvj (ORCPT ); Tue, 2 Jul 2019 05:51:39 -0400 Received: from mx1.redhat.com ([209.132.183.28]:43440 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727128AbfGBJvi (ORCPT ); Tue, 2 Jul 2019 05:51:38 -0400 Received: from smtp.corp.redhat.com (int-mx01.intmail.prod.int.phx2.redhat.com [10.5.11.11]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 184B1C02938A; Tue, 2 Jul 2019 09:51:38 +0000 (UTC) Received: from gondolin (dhcp-192-192.str.redhat.com [10.33.192.192]) by smtp.corp.redhat.com (Postfix) with ESMTP id 2E60A6F93D; Tue, 2 Jul 2019 09:51:37 +0000 (UTC) Date: Tue, 2 Jul 2019 11:51:34 +0200 From: Cornelia Huck To: Farhan Ali Cc: farman@linux.ibm.com, pasic@linux.ibm.com, linux-s390@vger.kernel.org, kvm@vger.kernel.org Subject: Re: [RFC v1 4/4] vfio-ccw: Don't call cp_free if we are processing a channel program Message-ID: <20190702115134.790f8891.cohuck@redhat.com> In-Reply-To: <31c3c29e3e9c4f0312f9363a1c3a5d22b74f68cb.1561997809.git.alifm@linux.ibm.com> References: <31c3c29e3e9c4f0312f9363a1c3a5d22b74f68cb.1561997809.git.alifm@linux.ibm.com> Organization: Red Hat GmbH MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.79 on 10.5.11.11 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.32]); Tue, 02 Jul 2019 09:51:38 +0000 (UTC) Sender: kvm-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: kvm@vger.kernel.org On Mon, 1 Jul 2019 12:23:46 -0400 Farhan Ali wrote: > There is a small window where it's possible that we could be working > on an interrupt (queued in the workqueue) and setting up a channel > program (i.e allocating memory, pinning pages, translating address). > This can lead to allocating and freeing the channel program at the > same time and can cause memory corruption. This can only happen if the interrupt is for a halt/clear operation, right? > > Let's not call cp_free if we are currently processing a channel program. > The only way we know for sure that we don't have a thread setting > up a channel program is when the state is set to VFIO_CCW_STATE_CP_PENDING. I have looked through the code again and I think you are right. > > Signed-off-by: Farhan Ali > --- > drivers/s390/cio/vfio_ccw_drv.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/drivers/s390/cio/vfio_ccw_drv.c b/drivers/s390/cio/vfio_ccw_drv.c > index 4e3a903..0357165 100644 > --- a/drivers/s390/cio/vfio_ccw_drv.c > +++ b/drivers/s390/cio/vfio_ccw_drv.c > @@ -92,7 +92,7 @@ static void vfio_ccw_sch_io_todo(struct work_struct *work) > (SCSW_ACTL_DEVACT | SCSW_ACTL_SCHACT)); > if (scsw_is_solicited(&irb->scsw)) { > cp_update_scsw(&private->cp, &irb->scsw); > - if (is_final) > + if (is_final && private->state == VFIO_CCW_STATE_CP_PENDING) Do we actually want to call cp_update_scsw() unconditionally? At this point, we know that we have a solicited interrupt; that may be for several reasons: - Interrupt for something we issued via ssch; it makes sense to update the scsw with the cpa address. - Interrupt for a csch; the cpa address will be unpredictable, even if we did a ssch before. cp_update_scsw() hopefully can deal with that? Given that its purpose is to translate the cpa back, any unpredictable value in the scsw should be fine in the end. - Interrupt for a hsch after we did a ssch; the cpa might be valid (see figure 16-6). - Interrupt for a hsch without a prior ssch; we'll end up with an unpredictable cpa, again. So I *think* we're fine with calling cp_update_scsw() in all cases, even if there's junk in the cpa of the scsw we get from the hardware. Opinions? > cp_free(&private->cp); > } > mutex_lock(&private->io_mutex);