The Software Delegated Exception Interface (SDEI) is an ARM specification for registering callbacks from the platform firmware into the OS. This is intended to be used to implement firmware-first RAS notifications, but also supports vendor-defined events and binding IRQs as events. The document is here: http://infocenter.arm.com/help/topic/com.arm.doc.den0054a/ARM_DEN0054A_Software_Delegated_Exception_Interface.pdf I anticipate once reviewed this series will go via the arm64 tree as it has an ever closer interaction with the arch code. Despite the bulk of the code being under /drivers/firmware/. The major change in v5 is the locking. Lockdep found a three-way issue via the hotplug state machine. (I argue it can't happen, but lockdep doesn't care.) Now the hotplug callbacks save nothing, and restore the OS-view of registered/enabled. This makes bound-interrupts harder to work with. I dropped Catalin's ack on all affected patches. SDEI interacts with Will's KTPI/kernel-unmapping series. These patches are based on v4.15-rc2 + v3 of that series[0], including the use-rodata diff[1]. Patches 15 and 16 contain the extra tramponline stuff. Christoffer was increasing the use of tpidr_el2 in EL2, which shares the first five patches, so if this is merged at the same time as his optimisations some co-ordination may be required. The regular boiler plate: This series (juggles some registers with KVM+VHE, then) adds a DT binding to trigger probing of the interface and support for the SDEI API. SDEI runs between adjacent exception levels, so events will always be delivered to EL2 if firmware is at EL3. For VHE hosts we run the SDEI event handler behind KVM's back with all exceptions masked. Once the handler has done its work we return to the appropriate vbar+irq entry. This allows KVM to world-switch and deliver any signals sent by the handler to Qemu/kvmtool. We do the same thing if we interrupt host EL0. If we interrupted code with interrupts masked, we use a different API call to return to the interrupted context. What about non-VHE KVM? If you don't have VHE support and boot at EL2, the kernel drops to EL1. This driver will print an error message then give up. This is because events would still be delivered to EL2 hitting either KVM, or the hyp-stub. Supporting this is complicated, but because the main use-case is RAS, and ARM v8.2's RAS extensions imply v8.1's Virtual Host Extensions, we can assume all platforms with SDEI will support VHE too. (I have some ideas on how to support non-VHE). Running the event handler behind VHE-KVM's back has some side effects: The event handler will blindly use any registers that are shared between the host and guest. The two that I think matter are TPIDR_EL1, and the debug state. The guest may have set MDSCR_EL1 so debug exceptions must remain masked. The guest's TPIDR_EL1 will be used by the event handler if it accesses per-cpu variables. This needs fixing. The first part of this series juggles KVMs use of TPIDR_EL2 so that we share it with the host on VHE systems. An equivalent change for 32bit is (still) on my todo list. (the alternative to this is to have a parody world switch in the SDEI event handler, but this would mean special casing interrupted guests, and be an ABI link to KVM.) Is this another begins-with-S RAS mechanism for arm64? Yes. Why? Any notification delivered as an exception will overwrite the exception registers. This is fatal for the running thread if it happens during entry.S's kernel_enter or kernel_exit. Instead of adding masking and routing controls, events are delivered to a registered address at a fixed exception level and don't change the exception registers when delivered. This series can be retrieved from: git://linux-arm.org/linux-jm.git -b sdei/v5/base Questions and contradictions welcome! Thanks, James [Changes since previous versions are noted on each patch] [0] https://lkml.org/lkml/2017/12/6/306 [1] https://lkml.org/lkml/2017/12/6/340 James Morse (16): KVM: arm64: Store vcpu on the stack during __guest_enter() KVM: arm/arm64: Convert kvm_host_cpu_state to a static per-cpu allocation KVM: arm64: Change hyp_panic()s dependency on tpidr_el2 arm64: alternatives: use tpidr_el2 on VHE hosts KVM: arm64: Stop save/restoring host tpidr_el1 on VHE Docs: dt: add devicetree binding for describing arm64 SDEI firmware firmware: arm_sdei: Add driver for Software Delegated Exceptions arm64: Add vmap_stack header file arm64: uaccess: Add PAN helper arm64: kernel: Add arch-specific SDEI entry code and CPU masking firmware: arm_sdei: Add support for CPU and system power states firmware: arm_sdei: add support for CPU private events arm64: acpi: Remove __init from acpi_psci_use_hvc() for use by SDEI firmware: arm_sdei: Discover SDEI support via ACPI arm64: mmu: add the entry tramolines start/end section markers into sections.h arm64: sdei: Add trampoline code for remapping the kernel .../devicetree/bindings/arm/firmware/sdei.txt | 42 + MAINTAINERS | 9 + arch/arm64/include/asm/alternative.h | 2 + arch/arm64/include/asm/assembler.h | 8 + arch/arm64/include/asm/kvm_host.h | 2 + arch/arm64/include/asm/mmu.h | 3 +- arch/arm64/include/asm/percpu.h | 11 +- arch/arm64/include/asm/sdei.h | 57 + arch/arm64/include/asm/sections.h | 1 + arch/arm64/include/asm/stacktrace.h | 3 + arch/arm64/include/asm/uaccess.h | 12 + arch/arm64/include/asm/vmap_stack.h | 26 + arch/arm64/kernel/Makefile | 1 + arch/arm64/kernel/acpi.c | 2 +- arch/arm64/kernel/alternative.c | 9 +- arch/arm64/kernel/asm-offsets.c | 5 + arch/arm64/kernel/cpufeature.c | 17 + arch/arm64/kernel/entry.S | 177 ++++ arch/arm64/kernel/irq.c | 13 +- arch/arm64/kernel/sdei.c | 235 +++++ arch/arm64/kernel/smp.c | 11 +- arch/arm64/kernel/suspend.c | 4 +- arch/arm64/kvm/hyp-init.S | 4 + arch/arm64/kvm/hyp/entry.S | 10 +- arch/arm64/kvm/hyp/hyp-entry.S | 18 +- arch/arm64/kvm/hyp/switch.c | 25 +- arch/arm64/kvm/hyp/sysreg-sr.c | 16 +- arch/arm64/mm/mmu.c | 2 - arch/arm64/mm/proc.S | 8 + drivers/firmware/Kconfig | 8 + drivers/firmware/Makefile | 1 + drivers/firmware/arm_sdei.c | 1091 ++++++++++++++++++++ include/linux/arm_sdei.h | 79 ++ include/linux/cpuhotplug.h | 1 + include/linux/psci.h | 3 +- include/uapi/linux/arm_sdei.h | 73 ++ virt/kvm/arm/arm.c | 18 +- 37 files changed, 1941 insertions(+), 66 deletions(-) create mode 100644 Documentation/devicetree/bindings/arm/firmware/sdei.txt create mode 100644 arch/arm64/include/asm/sdei.h create mode 100644 arch/arm64/include/asm/vmap_stack.h create mode 100644 arch/arm64/kernel/sdei.c create mode 100644 drivers/firmware/arm_sdei.c create mode 100644 include/linux/arm_sdei.h create mode 100644 include/uapi/linux/arm_sdei.h -- 2.15.0 -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
