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 49B31C47DDF for ; Tue, 30 Jan 2024 13:08:28 +0000 (UTC) Received: from boromir.ozlabs.org (localhost [IPv6:::1]) by lists.ozlabs.org (Postfix) with ESMTP id 4TPQTR064Vz3cXB for ; Wed, 31 Jan 2024 00:08:27 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=arm.com (client-ip=217.140.110.172; helo=foss.arm.com; envelope-from=mark.rutland@arm.com; receiver=lists.ozlabs.org) Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lists.ozlabs.org (Postfix) with ESMTP id 4TPQSx3DHDz3bWQ for ; Wed, 31 Jan 2024 00:07:57 +1100 (AEDT) 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 80839DA7; Tue, 30 Jan 2024 05:08:08 -0800 (PST) Received: from FVFF77S0Q05N (unknown [10.57.48.92]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 9D8453F762; Tue, 30 Jan 2024 05:07:20 -0800 (PST) Date: Tue, 30 Jan 2024 13:07:17 +0000 From: Mark Rutland To: Tong Tiangen Subject: Re: [PATCH v10 2/6] arm64: add support for machine check error safe Message-ID: References: <20240129134652.4004931-1-tongtiangen@huawei.com> <20240129134652.4004931-3-tongtiangen@huawei.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: 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: wangkefeng.wang@huawei.com, Catalin Marinas , Dave Hansen , linux-mm@kvack.org, Andrey Ryabinin , Alexander Potapenko , kasan-dev@googlegroups.com, "H. Peter Anvin" , Vincenzo Frascino , Will Deacon , x86@kernel.org, "Aneesh Kumar K.V" , Ingo Molnar , linux-arm-kernel@lists.infradead.org, "Naveen N. Rao" , Nicholas Piggin , Borislav Petkov , Alexander Viro , Thomas Gleixner , Dmitry Vyukov , Andrey Konovalov , linuxppc-dev@lists.ozlabs.org, Guohanjun , linux-kernel@vger.kernel.org, James Morse , Andrew Morton , Robin Murphy Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Tue, Jan 30, 2024 at 06:57:24PM +0800, Tong Tiangen wrote: > 在 2024/1/30 1:51, Mark Rutland 写道: > > On Mon, Jan 29, 2024 at 09:46:48PM +0800, Tong Tiangen wrote: > > > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c > > > index 55f6455a8284..312932dc100b 100644 > > > --- a/arch/arm64/mm/fault.c > > > +++ b/arch/arm64/mm/fault.c > > > @@ -730,6 +730,31 @@ static int do_bad(unsigned long far, unsigned long esr, struct pt_regs *regs) > > > return 1; /* "fault" */ > > > } > > > +static bool arm64_do_kernel_sea(unsigned long addr, unsigned int esr, > > > + struct pt_regs *regs, int sig, int code) > > > +{ > > > + if (!IS_ENABLED(CONFIG_ARCH_HAS_COPY_MC)) > > > + return false; > > > + > > > + if (user_mode(regs)) > > > + return false; > > > > This function is called "arm64_do_kernel_sea"; surely the caller should *never* > > call this for a SEA taken from user mode? > > In do_sea(), the processing logic is as follows: > do_sea() > { > [...] > if (user_mode(regs) && apei_claim_sea(regs) == 0) { > return 0; > } > [...] > //[1] > if (!arm64_do_kernel_sea()) { > arm64_notify_die(); > } > } > > [1] user_mode() is still possible to go here,If user_mode() goes here, > it indicates that the impact caused by the memory error cannot be > processed correctly by apei_claim_sea(). > > > In this case, only arm64_notify_die() can be used, This also maintains > the original logic of user_mode()'s processing. My point is that either: (a) The name means that this should *only* be called for SEAs from a kernel context, and the caller should be responsible for ensuring that. (b) The name is misleading, and the 'kernel' part should be removed from the name. I prefer (a), and if you head down that route it's clear that you can get rid of a bunch of redundant logic and remove the need for do_kernel_sea(), anyway, e.g. | static int do_sea(unsigned long far, unsigned long esr, struct pt_regs *regs) | { | const struct fault_info *inf = esr_to_fault_info(esr); | bool claimed = apei_claim_sea(regs) == 0; | unsigned long siaddr; | | if (claimed) { | if (user_mode(regs)) { | /* | * APEI claimed this as a firmware-first notification. | * Some processing deferred to task_work before ret_to_user(). | */ | return 0; | } else { | /* | * TODO: explain why this is correct. | */ | if ((current->flags & PF_KTHREAD) && | fixup_exception_mc(regs)) | return 0; | } | } | | if (esr & ESR_ELx_FnV) { | siaddr = 0; | } else { | /* | * The architecture specifies that the tag bits of FAR_EL1 are | * UNKNOWN for synchronous external aborts. Mask them out now | * so that userspace doesn't see them. | */ | siaddr = untagged_addr(far); | } | arm64_notify_die(inf->name, regs, inf->sig, inf->code, siaddr, esr); | | return 0; | } > > > + > > > + if (apei_claim_sea(regs) < 0) > > > + return false; > > > + > > > + if (!fixup_exception_mc(regs)) > > > + return false; > > > + > > > + if (current->flags & PF_KTHREAD) > > > + return true; > > > > I think this needs a comment; why do we allow kthreads to go on, yet kill user > > threads? What about helper threads (e.g. for io_uring)? > > If a memroy error occurs in the kernel thread, the problem is more > serious than that of the user thread. As a result, related kernel > functions, such as khugepaged, cannot run properly. kernel panic should > be a better choice at this time. > > Therefore, the processing scope of this framework is limited to the user > thread. That's reasonable, but needs to be explained in a comment. Also, as above, I think you haven't conisderd helper threads (e.g. io_uring), which don't have PF_KTHREAD set but do have PF_USER_WORKER set. I suspect those need the same treatment as kthreads. > > > + set_thread_esr(0, esr); > > > > Why do we set the ESR to 0? > > The purpose is to reuse the logic of arm64_notify_die() and set the > following parameters before sending signals to users: > current->thread.fault_address = 0; > current->thread.fault_code = err; Ok, but there's no need to open-code that. As per my above example, please continue to use the existing call to arm64_notify_die() rather than open-coding bits of it. Mark.