From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Subject: Re: [PATCH 0/3] arm64: kexec,kdump: fix boot failures on acpi-only system References: <20180615075623.13454-1-takahiro.akashi@linaro.org> From: James Morse Message-ID: <81a9a385-3b9f-113d-96f0-379be74c19f0@arm.com> Date: Fri, 15 Jun 2018 17:29:32 +0100 MIME-Version: 1.0 In-Reply-To: <20180615075623.13454-1-takahiro.akashi@linaro.org> Content-Language: en-US List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "kexec" Errors-To: kexec-bounces+dwmw2=infradead.org@lists.infradead.org To: AKASHI Takahiro Cc: mark.rutland@arm.com, lorenzo.pieralisi@arm.com, graeme.gregory@linaro.org, al.stone@linaro.org, ard.biesheuvel@linaro.org, catalin.marinas@arm.com, bhsharma@redhat.com, tbaicar@codeaurora.org, will.deacon@arm.com, linux-kernel@vger.kernel.org, hanjun.guo@linaro.org, sudeep.holla@arm.com, akpm@linux-foundation.org, dyoung@redhat.com, kexec@lists.infradead.org, linux-arm-kernel@lists.infradead.org Hi Akashi, Thanks for putting this together, On 15/06/18 08:56, AKASHI Takahiro wrote: > This patch series is a set of bug fixes to address kexec/kdump > failures which are sometimes observed on ACPI-only system and reported > in LAK-ML before. > > In short, the phenomena are: > 1. kexec'ed kernel can fail to boot because some ACPI table is corrupted > by a new kernel (or other data) being loaded into System RAM. Currently > kexec may possibly allocate space ignoring such "reserved" regions. > We will see no messages after "Bye!" > > 2. crash dump (kdump) kernel can fail to boot and get into panic due to > an alignment fault when accessing ACPI tables. This can happen because > those tables are not always properly aligned while they are mapped > non-cacheable (ioremap'ed) as they are not recognized as part of System > RAM under the current implementation. > > After discussing several possibilities to address those issues, > the agreed approach, in my understanding, is > * to add resource entries for every "reserved", i.e. memblock_reserve(), > regions to /proc/iomem. > (NOMAP regions, also marked as "reserved," remains at top-level for > backward compatibility.) This means user-space can tell the difference between reserved-system-ram and reserved-address-space. > * For case (1), user space (kexec-tools) should rule out such regions > in searching for free space for loaded data. ... but doesn't today, because it fails to account for second-level entries. We've always had second-level entries, so this is a user-space bug. We need both fixed to fix the issue. Our attempts to fix this just in the kernel reached a dead end, because Kdump needs to include reserved-system-ram, whereas kexec has to avoid it. User-space needs to be able to tell reserved-system-ram and reserved-address-space apart. Hence we need to expose that information, and pick it up in user-space. Patched-kernel and unpatch-user-space will work the same way it does today, as the additional reserved regions are ignored by user-space. Unpatched-kernel and patched-user-space will also work the same way it does today as the additional reserved regions are missing. I think this is the only way forwards on this issue... > * For case (2), the kernel should access ACPI tables by mapping > them with appropriate memory attributes described in UEFI memory map. > (This means that it doesn't require any changes in /proc/iomem, and > hence user space.) (this one is handled entirely in the kernel) Thanks, James _______________________________________________ kexec mailing list kexec@lists.infradead.org http://lists.infradead.org/mailman/listinfo/kexec