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[2620:137:e000::1:20]) by mx.google.com with ESMTP id c3-20020a637243000000b00517d81adf00si16679413pgn.624.2023.05.15.02.05.13; Mon, 15 May 2023 02:05:29 -0700 (PDT) Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20; Authentication-Results: mx.google.com; dkim=pass header.i=@linaro.org header.s=google header.b=Nnhqoxfg; spf=pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) smtp.mailfrom=linux-kernel-owner@vger.kernel.org; dmarc=pass (p=NONE sp=NONE dis=NONE) header.from=linaro.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S237826AbjEOIsM (ORCPT + 99 others); Mon, 15 May 2023 04:48:12 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:33088 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233666AbjEOIsK (ORCPT ); Mon, 15 May 2023 04:48:10 -0400 Received: from mail-vk1-xa34.google.com (mail-vk1-xa34.google.com [IPv6:2607:f8b0:4864:20::a34]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 9067AE75 for ; Mon, 15 May 2023 01:48:06 -0700 (PDT) Received: by mail-vk1-xa34.google.com with SMTP id 71dfb90a1353d-452f317e304so2904330e0c.2 for ; Mon, 15 May 2023 01:48:06 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linaro.org; s=google; t=1684140485; x=1686732485; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:from:to:cc:subject:date:message-id:reply-to; bh=1IBAn714ocZSNONKKCgtmlbf3ZTeCcDIYb+iNULuMvA=; b=NnhqoxfgqOuyxsLeWYsvVwYVWaqmx9+Uk271TUX/ZBTUJuoAPWFnST2GmpSj/GrW/5 dJRaXkrTkFQS/xfFBSKZRhWYdMTmVwn2OGZrOHkkPd0QF/Tl4sb93/SVQsQRc6WJC1Gl JhLQ3zqqAQ8Tz88GxdrNdMEX5VS4kBjgawH4z0caSMVMXiLBFheGfFqkWJ+vTbrn63Ti xv4oaRYfK8eb5+/ZkgWZ8R4TOvMONgk3FRBiqM7Ptkv3T83rTQjsO8loKXfNuiVAA71o a49D7KFseST/so+MPAn1Z3Wxuz30Tkj8WjRiHrcjLNWs+I8F5qU3XQpmX3aFR5HzYPTh I6iA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20221208; t=1684140485; x=1686732485; h=cc:to:subject:message-id:date:from:in-reply-to:references :mime-version:x-gm-message-state:from:to:cc:subject:date:message-id :reply-to; bh=1IBAn714ocZSNONKKCgtmlbf3ZTeCcDIYb+iNULuMvA=; b=LQz9mLPXblyebIN4V3MdVEV0pPA2o4OCNhclu8WQUdflT/m6CjcbKelsa+4Pi55+s6 k1I013pGcnaFGtsZA2V7LjRFJf+Y2a9XiDDzjwVag5cGUXINiL13s2fGGbCqlWYMh0D/ o15MuBaeKahdz7IQBGO8Od+gFD0aDStnv4n2XtLL8cpTTldDPu3ICz2C74rnjmK/SofK cmouizhcAECOV0AOhZd1iDCpDZ727LenZbvc0F0emit0fMkvdJce4bgxexkW55XsfHh6 p5mVwhie6cmi0bNUD8PBzr+FLyWfsZxIv3kDA0hINoQUK9DsC5HR+JcO6N34PLP+ZNsd VNPw== X-Gm-Message-State: AC+VfDzJz1SediwVAAHa6RVSnqT0Mqe8wgOn1NQU2VJ8/aK/X9Tj76m6 Wgy9qz6POhaSLlXXVw4+xiPhh34Bd46gi70AptJvJl2hy5xhm4I7OV0= X-Received: by 2002:a1f:d405:0:b0:44f:b9a8:be0c with SMTP id l5-20020a1fd405000000b0044fb9a8be0cmr11715084vkg.1.1684140485408; Mon, 15 May 2023 01:48:05 -0700 (PDT) MIME-Version: 1.0 References: <20230505173012.881083-1-etienne.carriere@linaro.org> <20230505173012.881083-3-etienne.carriere@linaro.org> In-Reply-To: From: Sumit Garg Date: Mon, 15 May 2023 14:17:54 +0530 Message-ID: Subject: Re: [PATCH v6 3/4] tee: optee: support tracking system threads To: Etienne Carriere Cc: linux-kernel@vger.kernel.org, linux-arm-kernel@lists.infradead.org, op-tee@lists.trustedfirmware.org, Jens Wiklander , Sudeep Holla , Cristian Marussi Content-Type: text/plain; charset="UTF-8" X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_NONE, SPF_HELO_NONE,SPF_PASS,T_SCC_BODY_TEXT_LINE autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, 12 May 2023 at 10:27, Etienne Carriere wrote: > > On Thu, 11 May 2023 at 13:31, Sumit Garg wrote: > > > > On Thu, 11 May 2023 at 13:49, Etienne Carriere > > wrote: > > > > > > On Thu, 11 May 2023 at 09:27, Sumit Garg wrote: > > > > (snip) > > > > > > > > > > > > > > > > +bool optee_cq_inc_sys_thread_count(struct optee_call_queue *cq) > > > > > > > > +{ > > > > > > > > + bool rc = false; > > > > > > > > + > > > > > > > > + mutex_lock(&cq->mutex); > > > > > > > > + > > > > > > > > + /* Leave at least 1 normal (non-system) thread */ > > > > > > > > > > > > > > IMO, this might be counter productive. As most kernel drivers open a > > > > > > > session during driver probe which are only released in the driver > > > > > > > release method. > > > > > > > > > > > > It is always the case? > > > > > > > > > > This answer of mine is irrelevant. Sorry, > > > > > Please read only the below comments of mine, especially: > > > > > | Note that an OP-TEE thread is not bound to a TEE session but rather > > > > > | bound to a yielded call to OP-TEE. > > > > > > > > > > > > > > > > > > If the kernel driver is built-in then the session is > > > > > > > never released. Now with system threads we would reserve an OP-TEE > > > > > > > thread for that kernel driver as well which will never be available to > > > > > > > regular user-space clients. > > > > > > > > > > > > That is not true. No driver currently requests their TEE thread to be > > > > > > a system thread. > > > > > > Only SCMI does because it needs to by construction. > > > > > > > > > > > > > > Yes that's true but what prevents future/current kernel TEE drivers > > > > from requesting a system thread once we have this patch-set landed. > > > > > > Only clients really needing this system_thread attribute should request it. > > > If they really need, the OP-TEE firmware in secure world should > > > provision sufficient thread context. > > > > How do we quantify it? We definitely need a policy here regarding > > normal vs system threads. > > > > One argument in favor of kernel clients requiring system threads could > > be that we don't want to compete with user-space for OP-TEE threads. > > Sorry I don't understand. What do you mean qualifying this? I mean we have to fairly allocate threads among system and non-system thread invocations. > In an ideal situation, we would have OP-TEE provisioned with largely > sufficient thread contexts. However there are systems with constraints > memory resource that do lower at most the number of OP-TEE thread > contexts. > Yeah, I think we are on the same page here. > > > > > > > > > > > > > > > > > > > > > > > > So I would rather suggest we only allow a > > > > > > > single system thread to be reserved as a starting point which is > > > > > > > relevant to this critical SCMI service. We can also make this upper > > > > > > > bound for system threads configurable with default value as 1 if > > > > > > > needed. > > > > > > > > > > Note that SCMI server can expose several SCMI channels (at most 1 per > > > > > SCMI protocol used) and each of them will need to request a > > > > > system_thread to TEE driver. > > > > > > > > > > Etienne > > > > > > > > > > > > > > > > > Reserving one or more system threads depends on the number of thread > > > > > > context provisioned by the TEE. > > > > > > Note that the implementation proposed here prevents Linux kernel from > > > > > > exhausting TEE threads so user space always has at least a TEE thread > > > > > > context left available. > > > > > > > > Yeah but on the other hand user-space clients which are comparatively > > > > larger in number than kernel clients. So they will be starved for > > > > OP-TEE thread availability. Consider a user-space client which needs > > > > to serve a lot of TLS connections just waiting for OP-TEE thread > > > > availability. > > > > > > Note that OP-TEE default configuration provisions (number of CPUs + 1) > > > thread context, so the situation is already present before these > > > changes on systems that embedded an OP-TEE without a properly tuned > > > configuration. As I said above, Linux kernel cannot be responsible for > > > the total number of thread contexts provisioned in OP-TEE. If the > > > overall system requires a lot of TEE thread contexts, one should embed > > > a suitable OP-TEE firmware. > > > > Wouldn't the SCMI deadlock problem be solved with just having a lot of > > OP-TEE threads? But we are discussing the system threads solution here > > to make efficient use of OP-TEE threads. The total number of OP-TEE > > threads is definitely in control of OP-TEE but the control of how to > > schedule and efficiently use them lies with the Linux OP-TEE driver. > > > > So, given our overall discussion in this thread, how about the upper > > bound for system threads being 50% of the total number of OP-TEE > > threads? > > What would be a shame if the system does not use any Linux kernel > client sessions, only userland clients. This information cannot be > knwon be the linux optee driver. > Instead of leaving at least 1 TEE thread context for regular session, > what if this change enforce 2? or 3? Which count? > I think 1 is a fair choice: it allows to support OP-TEE firmwares with > a very small thread context pool (when running in small secure > memory), embedding only 2 or 3 contextes. IMO, leaving only 1 thread for user-space will starve TLS based applications. How about the following change on top of this patchset? diff --git a/drivers/tee/optee/call.c b/drivers/tee/optee/call.c index 8b8181099da7..1deb5907d075 100644 --- a/drivers/tee/optee/call.c +++ b/drivers/tee/optee/call.c @@ -182,8 +182,8 @@ bool optee_cq_inc_sys_thread_count(struct optee_call_queue *cq) mutex_lock(&cq->mutex); - /* Leave at least 1 normal (non-system) thread */ - if (cq->res_sys_thread_count + 1 < cq->total_thread_count) { + /* Leave at least 50% for normal (non-system) threads */ + if (cq->res_sys_thread_count < cq->total_thread_count/2) { cq->free_normal_thread_count--; cq->res_sys_thread_count++; rc = true; > > > > > > > > > > > > > > > > > > > > > > Note that an OP-TEE thread is not bound to a TEE session but rather > > > > > > bound to a yielded call to OP-TEE. > > > > > > > > tee_client_open_session() > > > > -> optee_open_session() > > > > > > > > tee_client_system_session() > > > > -> optee_system_session() > > > > -> optee_cq_inc_sys_thread_count() <- At this point you > > > > reserve a system thread corresponding to a particular kernel client > > > > session > > > > > > > > All tee_client_invoke_func() invocations with a system thread capable > > > > session will use that reserved thread. > > > > > > > > tee_client_close_session() > > > > -> optee_close_session() > > > > -> optee_close_session_helper() > > > > -> optee_cq_dec_sys_thread_count() <- At this point the > > > > reserved system thread is released > > > > > > > > Haven't this tied the system thread to a particular TEE session? Or am > > > > I missing something? > > > > > > These changes do not define an overall single system thread. > > > If several sessions requests reservation of TEE system thread, has > > > many will be reserved. > > > Only the very sessions with its sys_thread attribute set will use a > > > reserved thread. If such a kernel client issues several concurrent > > > calls to OP-TEE over that session, it will indeed consume more > > > reserved system threads than what is actually reserved. Here I think > > > it is the responsibility of such client to open as many sessions as > > > requests. This is what scmi/optee driver does (see patch v6 4/4). An > > > alternative would be to have a ref count of sys_thread in session > > > contexts rather than a boolean value. I don't think it's worth it. > > > > Ah, I missed that during the review. The invocations with system > > threads should be limited by res_sys_thread_count in a similar manner > > as we do with normal threads via free_normal_thread_count. Otherwise, > > it's unfair for normal thread scheduling. > > > > I suppose there isn't any interdependency among SCMI channels itself > > such that a particular SCMI invocation can wait until the other SCMI > > invocation has completed. > > I think that would over complexify the logic. > We shouldn't allow system thread invocations to be greater than what is actually reserved count for system threads. One thing I am not able to understand here is why do you need a lot of system threads? Are SCMI operations too expensive? I suppose those should just involve configuring some register bits and using a single OP-TEE thread which is invoked sequentially should be enough. -Sumit > Note I will send a patch v8 series but feel free to continue the discussion. > It will at least address other comments you shared. > > Best regards, > Etienne > > > > > -Sumit