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=-8.7 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 9C796C34047 for ; Wed, 19 Feb 2020 13:04:25 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (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 583A524656 for ; Wed, 19 Feb 2020 13:04:25 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 583A524656 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 48Mybq1jnBzDqCW for ; Thu, 20 Feb 2020 00:04:23 +1100 (AEDT) Received: from ozlabs.org (bilbo.ozlabs.org [203.11.71.1]) (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 48My3m4xgGzDqB5 for ; Wed, 19 Feb 2020 23:40:04 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=ellerman.id.au Received: by ozlabs.org (Postfix, from userid 1034) id 48My3m00TPz9sSm; Wed, 19 Feb 2020 23:40:03 +1100 (AEDT) X-powerpc-patch-notification: thanks X-powerpc-patch-commit: 232ca1eecafed8c54491017f0612c33d8c742d74 In-Reply-To: <64a4aa44686e9fd4b01333401367029771d9b231.1581761633.git.christophe.leroy@c-s.fr> To: Christophe Leroy , Benjamin Herrenschmidt , Paul Mackerras , Erhard F. , Larry Finger From: Michael Ellerman Subject: Re: [PATCH v4] powerpc/32s: Fix DSI and ISI exceptions for CONFIG_VMAP_STACK Message-Id: <48My3m00TPz9sSm@ozlabs.org> Date: Wed, 19 Feb 2020 23:40:03 +1100 (AEDT) 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: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Sat, 2020-02-15 at 10:14:25 UTC, Christophe Leroy wrote: > hash_page() needs to read page tables from kernel memory. When entire > kernel memory is mapped by BATs, which is normally the case when > CONFIG_STRICT_KERNEL_RWX is not set, it works even if the page hosting > the page table is not referenced in the MMU hash table. > > However, if the page where the page table resides is not covered by > a BAT, a DSI fault can be encountered from hash_page(), and it loops > forever. This can happen when CONFIG_STRICT_KERNEL_RWX is selected > and the alignment of the different regions is too small to allow > covering the entire memory with BATs. This also happens when > CONFIG_DEBUG_PAGEALLOC is selected or when booting with 'nobats' > flag. > > Also, if the page containing the kernel stack is not present in the > MMU hash table, registers cannot be saved and a recursive DSI fault > is encountered. > > To allow hash_page() to properly do its job at all time and load the > MMU hash table whenever needed, it must run with data MMU disabled. > This means it must be called before re-enabling data MMU. To allow > this, registers clobbered by hash_page() and create_hpte() have to > be saved in the thread struct together with SRR0, SSR1, DAR and DSISR. > It is also necessary to ensure that DSI prolog doesn't overwrite > regs saved by prolog of the current running exception. That means: > - DSI can only use SPRN_SPRG_SCRATCH0 > - Exceptions must free SPRN_SPRG_SCRATCH0 before writing to the stack. > > This also fixes the Oops reported by Erhard when create_hpte() is > called by add_hash_page(). > > Due to prolog size increase, a few more exceptions had to get split > in two parts. > > Fixes: cd08f109e262 ("powerpc/32s: Enable CONFIG_VMAP_STACK") > Reported-by: Erhard F. > Link: https://bugzilla.kernel.org/show_bug.cgi?id=206501 > Signed-off-by: Christophe Leroy > Tested-by: Erhard F. > Tested-by: Larry Finger Applied to powerpc fixes, thanks. https://git.kernel.org/powerpc/c/232ca1eecafed8c54491017f0612c33d8c742d74 cheers