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=-2.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_2 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 DA155C43331 for ; Thu, 2 Apr 2020 16:03:29 +0000 (UTC) Received: from hemlock.osuosl.org (smtp2.osuosl.org [140.211.166.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id A82CB20757 for ; Thu, 2 Apr 2020 16:03:29 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A82CB20757 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.intel.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=iommu-bounces@lists.linux-foundation.org Received: from localhost (localhost [127.0.0.1]) by hemlock.osuosl.org (Postfix) with ESMTP id 76CC788B47; Thu, 2 Apr 2020 16:03:29 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from hemlock.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 3hZLVYKdgxmI; Thu, 2 Apr 2020 16:03:27 +0000 (UTC) Received: from lists.linuxfoundation.org (lf-lists.osuosl.org [140.211.9.56]) by hemlock.osuosl.org (Postfix) with ESMTP id 2658188ADB; Thu, 2 Apr 2020 16:03:27 +0000 (UTC) Received: from lf-lists.osuosl.org (localhost [127.0.0.1]) by lists.linuxfoundation.org (Postfix) with ESMTP id 09A26C1AE2; Thu, 2 Apr 2020 16:03:27 +0000 (UTC) Received: from whitealder.osuosl.org (smtp1.osuosl.org [140.211.166.138]) by lists.linuxfoundation.org (Postfix) with ESMTP id 3AFACC07FF for ; Thu, 2 Apr 2020 16:03:25 +0000 (UTC) Received: from localhost (localhost [127.0.0.1]) by whitealder.osuosl.org (Postfix) with ESMTP id 1F732883F2 for ; Thu, 2 Apr 2020 16:03:25 +0000 (UTC) X-Virus-Scanned: amavisd-new at osuosl.org Received: from whitealder.osuosl.org ([127.0.0.1]) by localhost (.osuosl.org [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id RETsbD1RN3uR for ; Thu, 2 Apr 2020 16:03:24 +0000 (UTC) X-Greylist: domain auto-whitelisted by SQLgrey-1.7.6 Received: from mga01.intel.com (mga01.intel.com [192.55.52.88]) by whitealder.osuosl.org (Postfix) with ESMTPS id 33399883EB for ; Thu, 2 Apr 2020 16:03:24 +0000 (UTC) IronPort-SDR: 5pgb0vztxVwAJ2dyI/xy97cLy3OFAveCB+dePjSl4hXJXejhgy/2j9p7hhsHtPpgsKuPeWS7Gx RJrpR1HHcDZg== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga006.fm.intel.com ([10.253.24.20]) by fmsmga101.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 02 Apr 2020 09:03:22 -0700 IronPort-SDR: +PTP4JYn8XK4q0RknKK20vQVFoXwKNg18a3TRxi854Bd++K8fHXvnUFPJ0LsjZVpMxxc77RLVV bFcOXo+vokeQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.72,336,1580803200"; d="scan'208";a="450978955" Received: from jacob-builder.jf.intel.com (HELO jacob-builder) ([10.7.199.155]) by fmsmga006.fm.intel.com with ESMTP; 02 Apr 2020 09:03:21 -0700 Date: Thu, 2 Apr 2020 09:09:09 -0700 From: Jacob Pan To: Jean-Philippe Brucker Subject: Re: [PATCH 00/10] IOASID extensions for guest SVA Message-ID: <20200402090909.4475d430@jacob-builder> In-Reply-To: <20200402122633.GC1176452@myrica> References: <1585158931-1825-1-git-send-email-jacob.jun.pan@linux.intel.com> <20200401140301.GJ882512@myrica> <20200401163842.09c8e1a6@jacob-builder> <20200402122633.GC1176452@myrica> Organization: OTC X-Mailer: Claws Mail 3.13.2 (GTK+ 2.24.30; x86_64-pc-linux-gnu) MIME-Version: 1.0 Cc: "Tian, Kevin" , Raj Ashok , Jean-Philippe Brucker , LKML , iommu@lists.linux-foundation.org, Alex Williamson , "Wu, Hao" , David Woodhouse , Jonathan Cameron X-BeenThere: iommu@lists.linux-foundation.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: Development issues for Linux IOMMU support List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: iommu-bounces@lists.linux-foundation.org Sender: "iommu" On Thu, 2 Apr 2020 14:26:33 +0200 Jean-Philippe Brucker wrote: > On Wed, Apr 01, 2020 at 04:38:42PM -0700, Jacob Pan wrote: > > On Wed, 1 Apr 2020 16:03:01 +0200 > > Jean-Philippe Brucker wrote: > > > > > Hi Jacob, > > > > > > On Wed, Mar 25, 2020 at 10:55:21AM -0700, Jacob Pan wrote: > > > > IOASID was introduced in v5.5 as a generic kernel allocator > > > > service for both PCIe Process Address Space ID (PASID) and ARM > > > > SMMU's Sub Stream ID. In addition to basic ID allocation, > > > > ioasid_set was introduced as a token that is shared by a group > > > > of IOASIDs. This set token can be used for permission checking > > > > but lack of some features needed by guest Shared Virtual > > > > Address (SVA). In addition, IOASID support for life cycle > > > > management is needed among multiple users. > > > > > > > > This patchset introduces two extensions to the IOASID code, > > > > 1. IOASID set operations > > > > 2. Notifications for IOASID state synchronization > > > > > > My main concern with this series is patch 7 changing the spinlock > > > to a mutex, which prevents SVA from calling ioasid_free() from > > > the RCU callback of MMU notifiers. Could we use atomic notifiers, > > > or do the FREE notification another way? > > > > > Maybe I am looking at the wrong code, I thought > > mmu_notifier_ops.free_notifier() is called outside spinlock with > > call_srcu(), which will be invoked in the thread context. > > in mmu_notifier.c mmu_notifier_put() > > spin_unlock(&mm->notifier_subscriptions->lock); > > > > call_srcu(&srcu, &subscription->rcu, > > mmu_notifier_free_rcu); > > free_notifier() is called from RCU callback, and according to > Documentation/RCU/checklist.txt: > > 5. If call_rcu() or call_srcu() is used, the callback function > will be called from softirq context. In particular, it cannot block. > > When applying the patch I get the sleep-in-atomic warning: > > [ 87.861793] BUG: sleeping function called from invalid context at > kernel/locking/mutex.c:935 [ 87.863293] in_atomic(): 1, > irqs_disabled(): 0, non_block: 0, pid: 74, name: kworker/6:1 > [ 87.863993] 2 locks held by kworker/6:1/74: [ 87.864493] #0: > ffffff885ac12538 ((wq_completion)rcu_gp){+.+.}-{0:0}, at: > process_one_work+0x740/0x1880 [ 87.865593] #1: ffffff88591efd30 > ((work_completion)(&sdp->work)){+.+.}-{0:0}, at: > process_one_work+0x740/0x1880 [ 87.866993] CPU: 6 PID: 74 Comm: > kworker/6:1 Not tainted 5.6.0-next-20200331+ #121 [ 87.867393] > Hardware name: FVP Base (DT) [ 87.867893] Workqueue: rcu_gp > srcu_invoke_callbacks [ 87.868393] Call trace: [ 87.868793] > dump_backtrace+0x0/0x310 [ 87.869293] show_stack+0x14/0x20 > [ 87.869693] dump_stack+0x124/0x180 [ 87.870193] > ___might_sleep+0x2ac/0x428 [ 87.870693] __might_sleep+0x88/0x168 > [ 87.871094] __mutex_lock+0xa0/0x1270 > [ 87.871593] mutex_lock_nested+0x1c/0x28 > [ 87.872093] ioasid_free+0x28/0x48 > [ 87.872493] io_mm_free+0x1d0/0x608 > [ 87.872993] mmu_notifier_free_rcu+0x74/0xe8 > [ 87.873393] srcu_invoke_callbacks+0x1d0/0x2c8 > [ 87.873893] process_one_work+0x858/0x1880 > [ 87.874393] worker_thread+0x314/0xcd0 > [ 87.874793] kthread+0x318/0x400 > [ 87.875293] ret_from_fork+0x10/0x18 > You are right, I was reading call_srcu comments too fast. I guess rcu callbacks are still in softirq not offloaded to kernel threads. * * The callback will be invoked from process context, but must * nevertheless be fast and must not block. */ So even atomic works in principle but not a good idea since it may take a long time. > > > > Anyway, if we have to use atomic. I tried atomic notifier first, > > there are two subscribers to the free event on x86. > > 1. IOMMU > > 2. KVM > > > > For #1, the problem is that in the free operation, VT-d driver > > needs to do a lot of clean up in thread context. > > - hold a mutex to traverse a list of devices > > - clear PASID entry and flush cache > > > > For #2, KVM might be able to deal with spinlocks for updating VMCS > > PASID translation table. +Hao > > > > Perhaps two solutions I can think of: > > 1. Use a cyclic IOASID allocator. The main reason of clean up at > > free is to prevent race with IOASID alloc. Similar to PID, 2M IOASID > > will take long time overflow. Then we can use atomic notifier and a > > deferred workqueue to do IOMMU cleanup. The downside is a large and > > growing PASID table, may not be a performance issue since it has > > TLB. > > That might be a problem for SMMU, which has 1024 * 64kB leaf PASID > tables, for a total of 64MB per endpoint if there is too much > fragmentation in the IOASID space. > OK. Not an option here :( > > 2. Let VFIO ensure free always happen after unbind. Then there is no > > need to do cleanup. But that requires VFIO to keep track of all the > > PASIDs within each VM. When the VM terminates, VFIO is responsible > > for the clean up. That was Yi's original proposal. I also tried to > > provide an IOASID set iterator for VFIO to free the IOASIDs within > > each VM/set, but the private data belongs to IOMMU driver. > > Not really my place to comment on this, but I find it nicer to use the > same gpasid_unbind() path when VFIO frees a PASID as when the guest > explicitly unbinds before freeing. > Might be the only option now. Thanks, Jacob > Thanks, > Jean > [Jacob Pan] _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu