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=-10.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 39F68C7618F for ; Wed, 17 Jul 2019 17:41:53 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 14DC3217F4 for ; Wed, 17 Jul 2019 17:41:53 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388518AbfGQRlw (ORCPT ); Wed, 17 Jul 2019 13:41:52 -0400 Received: from foss.arm.com ([217.140.110.172]:49536 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725948AbfGQRlv (ORCPT ); Wed, 17 Jul 2019 13:41:51 -0400 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 3C29328; Wed, 17 Jul 2019 10:41:50 -0700 (PDT) Received: from [10.1.196.105] (eglon.cambridge.arm.com [10.1.196.105]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A26D43F71F; Wed, 17 Jul 2019 10:41:47 -0700 (PDT) Subject: Re: [PATCH RFC 2/4] arm64: mm: Add RAS extension system register check to SEA handling To: Tyler Baicar OS , "mark.rutland@arm.com" Cc: "lorenzo.pieralisi@arm.com" , "catalin.marinas@arm.com" , "sudeep.holla@arm.com" , "rjw@rjwysocki.net" , "linux-kernel@vger.kernel.org" , "Matteo.Carlini@arm.com" , "linux-acpi@vger.kernel.org" , "tony.luck@intel.com" , "bp@alien8.de" , "guohanjun@huawei.com" , "Andrew.Murray@arm.com" , Open Source Submission , "lenb@kernel.org" , "will@kernel.org" , "linux-arm-kernel@lists.infradead.org" , "linux-edac@vger.kernel.org" References: <1562086280-5351-1-git-send-email-baicar@os.amperecomputing.com> <1562086280-5351-3-git-send-email-baicar@os.amperecomputing.com> From: James Morse Message-ID: <80d7ad43-5426-3117-0445-0add5bc008f5@arm.com> Date: Wed, 17 Jul 2019 18:41:44 +0100 User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:60.0) Gecko/20100101 Thunderbird/60.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-GB Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Tyler, On 11/07/2019 05:14, Tyler Baicar OS wrote: > On Tue, Jul 9, 2019 at 8:52 PM Tyler Baicar OS wrote: >> On Mon, Jul 8, 2019 at 10:10 AM James Morse wrote: >>> On 02/07/2019 17:51, Tyler Baicar OS wrote: >>>> @@ -632,6 +633,8 @@ static int do_sea(unsigned long addr, unsigned int esr, struct pt_regs *regs) >>>> >>>> inf = esr_to_fault_info(esr); >>>> >>>> + arch_arm_ras_report_error(); >>>> + >>>> /* >>>> * Return value ignored as we rely on signal merging. >>>> * Future patches will make this more robust. >>>> >>> >>> If we interrupted a preemptible context, do_sea() is preemptible too... This means we >>> can't know if we're still running on the same CPU as the one that took the external-abort. >>> (until this series, it hasn't mattered). >>> >>> Fixing this means cramming something into entry.S's el1_da, as this may unmask interrupts >>> before calling do_mem_abort(). But its going to be ugly because some of do_mem_abort()s >>> ESR values need to be preemptible because they sleep, e.g. page-faults calling >>> handle_mm_fault(). >>> For do_sea(), do_exit() will 'fix' the preempt count if we kill the thread, but if we >>> don't, it still needs to be balanced. Doing all this in assembly is going to be unreadable! >>> >>> Mark Rutland has a series to move the entry assembly into C [0]. Based on that that it >>> should be possible for the new el1_abort() to spot a Synchronous-External-Abort ESR, and >>> wrap the do_mem_abort() with preempt enable/disable, before inheriting the flags. (which >>> for synchronous exceptions, I think we should always do) >>> >>> [0] https://git.kernel.org/pub/scm/linux/kernel/git/mark/linux.git/log/?h=arm64/entry-deasm >> Good catch! I didn't think the synchronous route was preemptible. >> I wasn't seeing this issue when testing this on emulation, but I was able to >> test and prove the issue on a Neoverse N1 SDP: >> >> root@genericarmv8:~# echo 0x100000000 > /proc/cached_read >> [ 42.985622] Reading from address 0x100000000 >> [ 42.989893] WARNING: CPU: 0 PID: 2812 at /home/tyler/neoverse/arm-reference- >> platforms/linux/arch/arm64/kernel/cpufeature.c:1940 this_cpu_has_cap+0x68/0x78 [...] >> [ 43.175647] Internal error: synchronous external abort: 96000410 [#1] >> PREEMPT SMP [...] >> I'll pull Mark's series in and add the preempt enable/disable around the call >> to do_mem_abort() in el1_abort() and test that out! > > I was able to pull in the series mentioned [0] and add a patch to wrap > do_mem_abort with preempt disable/enable and the warning has gone away. Great. I spoke to Mark who commented he hadn't had the time to finish rebasing it onto for-next/core. (which I guess is why it didn't get posted!). I've taken a stab at picking out the 'synchronous' parts and rebasing it onto arm64's for-next/core. That tree is here: http://www.linux-arm.org/git?p=linux-jm.git;a=shortlog;h=refs/heads/deasm_sync_only/v0 (this should save you doing the rebase) I'll aim to rebase/retest and post it next week. > diff --git a/arch/arm64/kernel/entry-common.c b/arch/arm64/kernel/entry-common.c > index 43aa78331e72..26cdf7db511a 100644 > --- a/arch/arm64/kernel/entry-common.c > +++ b/arch/arm64/kernel/entry-common.c > @@ -118,7 +118,25 @@ static void el1_abort(struct pt_regs *regs, unsigned long esr) el0_ia/da will have the same problem. > unsigned long far = read_sysreg(far_el1); > local_daif_inherit(regs); > far = untagged_addr(far); > - do_mem_abort(far, esr, regs); > + > + switch (esr & ESR_ELx_FSC) { > + case ESR_ELx_FSC_EXTABT: // Synchronous External Abort > + case 0x14: // SEA level 0 translation table walk > + case 0x15: // SEA level 1 translation table walk > + case 0x16: // SEA level 2 translation table walk > + case 0x17: // SEA level 3 translation table walk > + case 0x18: // Synchronous ECC error > + case 0x1c: // SECC level 0 translation table walk > + case 0x1d: // SECC level 1 translation table walk > + case 0x1e: // SECC level 2 translation table walk > + case 0x1f: // SECC level 3 translation table walk Hex numbers, lovely. KVM has a helper for this, can we move/clean that so we can use it here? > + preempt_disable(); This is still too late. You can take an interrupt between local_daif_inherit() and be migrated, before you call preempt_disable() here. The local_daif_inherit() may need to move into the switch() too. It may be simpler to fold the 'is_extabt(esr)' check into el1_sync, so that these bypass el1_abort() and call do_sea() directly, which could then handle the far-read, preempt-count and daif-inherit itself. I prefer ... whichever looks cleanest! > + do_mem_abort(far, esr, regs); > + preempt_enable(); > + break; > + default: > + do_mem_abort(far, esr, regs); > + }; > } Thanks, James