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 lists.ozlabs.org (lists.ozlabs.org [112.213.38.117]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 636C5C07CB1 for ; Wed, 29 Nov 2023 13:24:39 +0000 (UTC) Authentication-Results: lists.ozlabs.org; dkim=fail reason="signature verification failed" (2048-bit key; unprotected) header.d=ellerman.id.au header.i=@ellerman.id.au header.a=rsa-sha256 header.s=201909 header.b=fts1g4mc; dkim-atps=neutral Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4SgKmk0vC0z3vmD for ; Thu, 30 Nov 2023 00:24:38 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; dkim=pass (2048-bit key; unprotected) header.d=ellerman.id.au header.i=@ellerman.id.au header.a=rsa-sha256 header.s=201909 header.b=fts1g4mc; dkim-atps=neutral Received: from gandalf.ozlabs.org (mail.ozlabs.org [IPv6:2404:9400:2221:ea00::3]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 4SgKh96X9qz3d8y for ; Thu, 30 Nov 2023 00:20:41 +1100 (AEDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=ellerman.id.au; s=201909; t=1701264041; bh=OKAi9zgo4g/bQmTQBdSLrAuecjEinmMfHE8kTBND2a4=; h=From:To:Cc:Subject:In-Reply-To:References:Date:From; b=fts1g4mcy4taQ5OHfOyhbSUVs1VaZeepZzt/j252B/6z2thNSOWbTMrW4blrtMRLD /61egxE82F1NBJmTzR44XvykIn11Tc8rG1CSoiAxOpLoShN93wrVpl4WdCm1C6MFr0 yJG2u/WYaLk5ayZuhO0TcB8JF+du+4JaVqUqFNN12wEmfx6N0q+kYrGu4lht3j9Vky mwuGKJVHIvQbMZY+xqGdzAm94IF/Uoo+x6sIfaZ9vAT6muBfcJkGRztj5lPZraHnA9 TNkFCzIzDs0vCyqzZzlkHgL4EhMTyoYD1DVd04NAtqkG5IiM8yfm9HP4/1XWAgAimX Efe/nAtm9uYsA== Received: from authenticated.ozlabs.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by mail.ozlabs.org (Postfix) with ESMTPSA id 4SgKh91f3Hz4x5q; Thu, 30 Nov 2023 00:20:41 +1100 (AEDT) From: Michael Ellerman To: Nathan Lynch , Nathan Lynch via B4 Relay , Nicholas Piggin Subject: Re: [PATCH v4 05/13] powerpc/rtas: Facilitate high-level call sequences In-Reply-To: <87jzq11nsj.fsf@li-e15d104c-2135-11b2-a85c-d7ef17e56be6.ibm.com> References: <20231117-papr-sys_rtas-vs-lockdown-v4-0-b794d8cb8502@linux.ibm.com> <20231117-papr-sys_rtas-vs-lockdown-v4-5-b794d8cb8502@linux.ibm.com> <87sf4p33zg.fsf@mail.lhotse> <87jzq11nsj.fsf@li-e15d104c-2135-11b2-a85c-d7ef17e56be6.ibm.com> Date: Thu, 30 Nov 2023 00:20:40 +1100 Message-ID: <874jh43dcn.fsf@mail.lhotse> MIME-Version: 1.0 Content-Type: text/plain X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: tyreld@linux.ibm.com, Michal =?utf-8?Q?Such=C3=A1nek?= , linuxppc-dev@lists.ozlabs.org, gcwilson@linux.ibm.com Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Nathan Lynch writes: > Michael Ellerman writes: > >> Nathan Lynch via B4 Relay >> writes: >>> From: Nathan Lynch >>> >>> On RTAS platforms there is a general restriction that the OS must not >>> enter RTAS on more than one CPU at a time. This low-level >>> serialization requirement is satisfied by holding a spin >>> lock (rtas_lock) across most RTAS function invocations. >> ... >>> diff --git a/arch/powerpc/kernel/rtas.c b/arch/powerpc/kernel/rtas.c >>> index 1fc0b3fffdd1..52f2242d0c28 100644 >>> --- a/arch/powerpc/kernel/rtas.c >>> +++ b/arch/powerpc/kernel/rtas.c >>> @@ -581,6 +652,28 @@ static const struct rtas_function *rtas_token_to_function(s32 token) >>> return NULL; >>> } >>> >>> +static void __rtas_function_lock(struct rtas_function *func) >>> +{ >>> + if (func && func->lock) >>> + mutex_lock(func->lock); >>> +} >> >> This is obviously going to defeat most static analysis tools. > > I guess it's not that obvious to me :-) Is it because the mutex_lock() > is conditional? I'll improve this if it's possible. Well maybe I'm not giving modern static analysis tools enough credit :) But what I mean that it's not easy to reason about what the function does in isolation. ie. all you can say is that it may or may not lock a mutex, and you can't say which mutex. >> I assume lockdep is OK with it though? > > Seems to be, yes. OK. cheers