James, Thank you for follow-up explanation. I have nothing to add :) -Takahiro AKASHI On Fri, Jun 15, 2018 at 05:29:32PM +0100, James Morse wrote: > 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@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
