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 33235C433EF for ; Mon, 24 Jan 2022 12:30:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S239810AbiAXMaW (ORCPT ); Mon, 24 Jan 2022 07:30:22 -0500 Received: from gloria.sntech.de ([185.11.138.130]:53154 "EHLO gloria.sntech.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S241502AbiAXMaV (ORCPT ); Mon, 24 Jan 2022 07:30:21 -0500 Received: from ip5b412258.dynamic.kabel-deutschland.de ([91.65.34.88] helo=diego.localnet) by gloria.sntech.de with esmtpsa (TLS1.3:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.92) (envelope-from ) id 1nByU4-0002so-3s; Mon, 24 Jan 2022 13:30:08 +0100 From: Heiko =?ISO-8859-1?Q?St=FCbner?= To: Atish Patra Cc: Palmer Dabbelt , Paul Walmsley , Albert Ou , linux-riscv , devicetree , "linux-kernel@vger.kernel.org List" , Rob Herring , Wei Fu , liush , Guo Ren , Anup Patel , Drew Fustini , Christoph Hellwig , Arnd Bergmann , Chen-Yu Tsai , Maxime Ripard , Daniel Lustig , Greg Favor , Andrea Mondelli , Jonathan Behrens , Xinhaoqu , Bill Huffman , Nick Kossifidis , Allen Baum , Josh Scheid , Richard Trauben , Samuel Holland , Christoph Muellner , Philipp Tomsich Subject: Re: [PATCH v5 01/14] riscv: only use IPIs to handle cache-flushes on remote cpus Date: Mon, 24 Jan 2022 13:30:06 +0100 Message-ID: <10651919.N8281ZbHTu@diego> In-Reply-To: References: <20220121163618.351934-1-heiko@sntech.de> <20220121163618.351934-2-heiko@sntech.de> MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="us-ascii" Precedence: bulk List-ID: X-Mailing-List: devicetree@vger.kernel.org Hi Atish, Am Samstag, 22. Januar 2022, 04:45:52 CET schrieb Atish Patra: > On Fri, Jan 21, 2022 at 8:37 AM Heiko Stuebner wrote: > > > > Right now, the flush_icache functions always use the SBI remote-fence > > when SBI is available, leaving using IPIs as a fallback mechanism. > > > > IPIs on the other hand are more flexible, as the ipi_ops are initially > > set to go through SBI but later will be overwritten to go through the > > ACLINT/CLINT. > > > > In a discussion we had, Nick was of the opinion that "In general we > > should prefer doing IPIs on S-mode through CLINT instead of going > > through SBI/M-mode, > > Yes. Once Anup's ACLINT drivers are merged, that should be the > preferred approach. > > https://github.com/avpatel/linux/commit/416c667fd77d6f1fc310cbf727ec127aaf96cae2 > > >so IMHO we should only be using > > on_each_cpu_mask(ipi_remote_fence_i) on flush_icache_all()/ > > flush_icache_mm() and remove any explicit calls to sbi_remote_fence_i(), > > That's a bit confusing because we will be using SBI calls for all other fences > while using IPIs for fence.i > > > because this way we continue using SBI for doing remote fences even after > > CLINT/ACLINT driver is registered, instead of using direct IPIs through > > CLINT/ACLINT." > > > > So follow this suggestion and just do ipi calls to have the proper kernel > > parts do them, > > > > This also fixes the null-ptr dereference happening when flush_icache_all() > > is called before sbi_init(). > > > > IMHO, this series should only fix the null-ptr dereference issue. > The IPI based fence (for all) should only be disabled along with the > ACLINT driver > that actually enables S-mode IPIs. ok, I'll roll this back to simply fixing the null-ptr issue. Meanwhile I even found a nicer solution without actually touching the cachflush code. Without sbi_init() we can assume that we're still before smp bringup, so the local_flush_icache_all() in flush_icache_all() will do the trick just fine and sbi_remote_fence_i() simply just needs to be an empty function until sbi is initialized. Heiko > > > Suggested-by: Nick Kossifidis > > Signed-off-by: Heiko Stuebner > > --- > > arch/riscv/mm/cacheflush.c | 8 +------- > > 1 file changed, 1 insertion(+), 7 deletions(-) > > > > diff --git a/arch/riscv/mm/cacheflush.c b/arch/riscv/mm/cacheflush.c > > index 6cb7d96ad9c7..c35375cd52ec 100644 > > --- a/arch/riscv/mm/cacheflush.c > > +++ b/arch/riscv/mm/cacheflush.c > > @@ -17,11 +17,7 @@ static void ipi_remote_fence_i(void *info) > > void flush_icache_all(void) > > { > > local_flush_icache_all(); > > - > > - if (IS_ENABLED(CONFIG_RISCV_SBI)) > > - sbi_remote_fence_i(NULL); > > - else > > - on_each_cpu(ipi_remote_fence_i, NULL, 1); > > + on_each_cpu(ipi_remote_fence_i, NULL, 1); > > } > > EXPORT_SYMBOL(flush_icache_all); > > > > @@ -66,8 +62,6 @@ void flush_icache_mm(struct mm_struct *mm, bool local) > > * with flush_icache_deferred(). > > */ > > smp_mb(); > > - } else if (IS_ENABLED(CONFIG_RISCV_SBI)) { > > - sbi_remote_fence_i(&others); > > } else { > > on_each_cpu_mask(&others, ipi_remote_fence_i, NULL, 1); > > } > > -- > > 2.30.2 > > > > > > _______________________________________________ > > linux-riscv mailing list > > linux-riscv@lists.infradead.org > > http://lists.infradead.org/mailman/listinfo/linux-riscv > > > >