From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755494AbdEHR3M (ORCPT ); Mon, 8 May 2017 13:29:12 -0400 Received: from foss.arm.com ([217.140.101.70]:45844 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755203AbdEHR3J (ORCPT ); Mon, 8 May 2017 13:29:09 -0400 Message-ID: <5910AAB8.8070703@arm.com> Date: Mon, 08 May 2017 18:28:24 +0100 From: James Morse User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Icedove/31.6.0 MIME-Version: 1.0 To: Tyler Baicar CC: christoffer.dall@linaro.org, marc.zyngier@arm.com, pbonzini@redhat.com, rkrcmar@redhat.com, linux@armlinux.org.uk, catalin.marinas@arm.com, will.deacon@arm.com, rjw@rjwysocki.net, lenb@kernel.org, matt@codeblueprint.co.uk, robert.moore@intel.com, lv.zheng@intel.com, nkaje@codeaurora.org, zjzhang@codeaurora.org, mark.rutland@arm.com, akpm@linux-foundation.org, eun.taik.lee@samsung.com, sandeepa.s.prabhu@gmail.com, labbott@redhat.com, shijie.huang@arm.com, rruigrok@codeaurora.org, paul.gortmaker@windriver.com, tn@semihalf.com, fu.wei@linaro.org, rostedt@goodmis.org, bristot@redhat.com, linux-arm-kernel@lists.infradead.org, kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org, linux-kernel@vger.kernel.org, linux-acpi@vger.kernel.org, linux-efi@vger.kernel.org, devel@acpica.org, Suzuki.Poulose@arm.com, punit.agrawal@arm.com, astone@redhat.com, harba@codeaurora.org, hanjun.guo@linaro.org, john.garry@huawei.com, shiju.jose@huawei.com, joe@perches.com, bp@alien8.de, rafael@kernel.org, tony.luck@intel.com, gengdongjiu@huawei.com, xiexiuqi@huawei.com Subject: Re: [PATCH V15 06/11] acpi: apei: handle SEA notification type for ARMv8 References: <1492556723-9189-1-git-send-email-tbaicar@codeaurora.org> <1492556723-9189-7-git-send-email-tbaicar@codeaurora.org> In-Reply-To: <1492556723-9189-7-git-send-email-tbaicar@codeaurora.org> Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Hi Tyler, On 19/04/17 00:05, Tyler Baicar wrote: > ARM APEI extension proposal added SEA (Synchronous External Abort) > notification type for ARMv8. > Add a new GHES error source handling function for SEA. If an error > source's notification type is SEA, then this function can be registered > into the SEA exception handler. That way GHES will parse and report > SEA exceptions when they occur. > An SEA can interrupt code that had interrupts masked and is treated as > an NMI. To aid this the page of address space for mapping APEI buffers > while in_nmi() is always reserved, and ghes_ioremap_pfn_nmi() is > changed to use the helper methods to find the prot_t to map with in > the same way as ghes_ioremap_pfn_irq(). > diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c > index b74d8b7..10013ff 100644 > --- a/arch/arm64/mm/fault.c > +++ b/arch/arm64/mm/fault.c > @@ -518,6 +520,17 @@ static int do_sea(unsigned long addr, unsigned int esr, struct pt_regs *regs) > pr_err("Synchronous External Abort: %s (0x%08x) at 0x%016lx\n", > inf->name, esr, addr); > > + /* > + * Synchronous aborts may interrupt code which had interrupts masked. > + * Before calling out into the wider kernel tell the interested > + * subsystems. > + */ > + if (IS_ENABLED(CONFIG_ACPI_APEI_SEA)) { > + nmi_enter(); > + ghes_notify_sea(); > + nmi_exit(); > + } > + > info.si_signo = SIGBUS; > info.si_errno = 0; > info.si_code = 0; I was tidying up the masking/unmasking in entry.S, something I wasn't aware of that leads to a bug: entry.S will unmask interrupts for instruction/data aborts that came from a context with interrupts enabled. This makes sense for get_user() and friends... For do_sea() we pull nmi_enter() as this can interrupt interrupts-masked code, such as APEI, but if we end up in here with interrupts unmasked we can take an IRQ from this 'NMI' context, which will inherit the in_nmi() and could lead to the deadlock we were originally trying to avoid. Teaching entry.S to spot external aborts is messy. I think the two choices are to either mask interrupts when calling nmi_enter() (as these things should be mutually exclusive), or to conditionally call nmi_enter() based on interrupts_enabled(regs). I prefer the second one as it matches the notify_sea() while interruptible that happens when KVM takes one of these. Thanks, James