| Message ID | 20180615075623.13454-1-takahiro.akashi@linaro.org |
|---|---|
| Headers | show |
| Series | arm64: kexec,kdump: fix boot failures on acpi-only system | expand |
Hi Akashi, Thanks for the patchset - we have been waiting for quite some time for this fix so that crashkernel can boot on arm64 machines which support boot'ing via ACPI tables. I have tested this on my huawei-taishan arm64 board, so: Tested-by: Bhupesh Sharma <bhsharma@redhat.com> BTW, if possible I would suggest to use: Reported-by: Bhupesh Sharma <bhsharma@redhat.com> rather than: Reported-by: Bhupesh Sharma <bhupesh.linux@gmail.com> Thanks, Bhupesh On Fri, Jun 15, 2018 at 1:26 PM, AKASHI Takahiro <takahiro.akashi@linaro.org> wrote: > # apologies for a bit late updates > > 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.) > * For case (1), user space (kexec-tools) should rule out such regions > in searching for free space for loaded data. > * 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.) > > Please find past discussions about /proc/iomem in [1]. > > Patch#1 addresses kexec case, for which you are also required to update > user space. See necessary patches in [2]. If you want to review Patch#1, > please also take a look at and review [2]. > > Patch#2 and #3 addresses kdump case. This is a revised version after > Ard's comments.[3] > > [1] http://lists.infradead.org/pipermail/linux-arm-kernel/2018-March/565980.html > [2] https://git.linaro.org/people/takahiro.akashi/kexec-tools.git arm64/resv_mem > [3] http://lists.infradead.org/pipermail/linux-arm-kernel/2018-April/573655.html > > AKASHI Takahiro (2): > arm64: acpi,efi: fix alignment fault in accessing ACPI tables at kdump > init: map UEFI memory map early if on arm or arm64 > > James Morse (1): > arm64: export memblock_reserve()d regions via /proc/iomem > > arch/arm64/include/asm/acpi.h | 23 ++++++++++++------ > arch/arm64/kernel/acpi.c | 11 +++------ > arch/arm64/kernel/setup.c | 38 ++++++++++++++++++++++++++++++ > drivers/firmware/efi/arm-runtime.c | 27 ++++++++++----------- > init/main.c | 3 +++ > 5 files changed, 72 insertions(+), 30 deletions(-) > > -- > 2.17.0 >
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
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