On 26/08/2019 22:25, Pavel Tatashin wrote: > On Mon, Aug 26, 2019 at 3:13 PM Marc Zyngier <maz@xxxxxxxxxx> wrote: >> >> On Mon, 26 Aug 2019 15:00:50 -0400 >> Pavel Tatashin <pasha.tatashin@xxxxxxxxxx> wrote: >> >>> Marc Zyngier added the support for kexec and GICv3 for EFI based systems. >>> However, it is still not possible todo on systems with device trees. >>> >>> Here is EFI fixes from Marc: >>> https://lore.kernel.org/lkml/20180921195954.21574-1-marc.zyngier@xxxxxxx >>> >>> For Device Tree variant: lets allow reserve a memory region in interrupt >>> controller node, and use this property to allocate interrupt tables. >> >> There is no such thing as a "device tree variant". As long as your >> bootloader implements EFI, everything will work correctly, whether >> you're using DT, ACPI, or the anything else. >> >> This already works today, without any need to add anything to the >> kernel (I have systems using EDK II and u-boot, both implementing EFI, >> and I'm able to kexec without any issue). If your bootloader doesn't >> support EFI, here's a good opportunity to implement it! > > Hi Marc, > > Thank you very much for looking at this work. > > Running Linux without EFI is common, and there are scenarios which > make it appropriate. As I understand most of embedded linux do not > have EFI enabled, and thus I do not see a reason why we would not > support a first class feature of Linux (kexec) on non-EFI bootloaders. Define "most". All the arm64 systems I have around (and trust me, that's quite a number of them) can either use u-boot, which has more than enough EFI support to use this functionality, or use EDK-II natively. > We (Microsoft) have a small highly secure device with a high uptime > requirement. The device also has PCIe and thus GICv3. The update for PCIe doesn't imply GICv3 at all. > this device relies on kexec. For a number of reasons, it was decided > to use U-Boot and Linux without EFI enabled. One of those reasons is > to improve boot performance, enabling EFI in U-Boot alone reduces the > boot performance by half a second. Our total reboot budget is under a > second which makes that half a second unacceptable. Also, adding EFI > support to kernel increases its size and there are security > implications from enabling more code both in U-Boot and Linux. You're are missing the point. kexec with EFI has 0 overhead (no non-kernel EFI code gets executed), doesn't impact your time budget, and only relies on a single in-memory table. This can be pretty trivially provided by the dumbest EFI shim. All you are describing above is a set of self imposed limitations in your bootloader, which you are fully in control of. So instead of reinventing a square wheel, I suggest you adopt the existing implementation. Another reason not to do this is interoperability: I want to be able to kexec whatever Linux kernel I want, without having to cope with all flavours of the same functionality. Effectively, the EFI table is a private ABI between two Linux kernels. We're not changing it. M. -- Jazz is not dead, it just smells funny... _______________________________________________ kexec mailing list kexec@xxxxxxxxxxxxxxxxxxx http://lists.infradead.org/mailman/listinfo/kexec
