From: Joerg Roedel <jroedel@xxxxxxx> Hi, here are changes to enable kexec/kdump in SEV-ES guests. The biggest problem for supporting kexec/kdump under SEV-ES is to find a way to hand the non-boot CPUs (APs) from one kernel to another. Without SEV-ES the first kernel parks the CPUs in a HLT loop until they get reset by the kexec'ed kernel via an INIT-SIPI-SIPI sequence. For virtual machines the CPU reset is emulated by the hypervisor, which sets the vCPU registers back to reset state. This does not work under SEV-ES, because the hypervisor has no access to the vCPU registers and can't make modifications to them. So an SEV-ES guest needs to reset the vCPU itself and park it using the AP-reset-hold protocol. Upon wakeup the guest needs to jump to real-mode and to the reset-vector configured in the AP-Jump-Table. The code to do this is the main part of this patch-set. It works by placing code on the AP Jump-Table page itself to park the vCPU and for jumping to the reset vector upon wakeup. The code on the AP Jump Table runs in 16-bit protected mode with segment base set to the beginning of the page. The AP Jump-Table is usually not within the first 1MB of memory, so the code can't run in real-mode. The AP Jump-Table is the best place to put the parking code, because the memory is owned, but read-only by the firmware and writeable by the OS. Only the first 4 bytes are used for the reset-vector, leaving the rest of the page for code/data/stack to park a vCPU. The code can't be in kernel memory because by the time the vCPU wakes up the memory will be owned by the new kernel, which might have overwritten it already. The other patches add initial GHCB Version 2 protocol support, because kexec/kdump need the MSR-based (without a GHCB) AP-reset-hold VMGEXT, which is a GHCB protocol version 2 feature. The kexec'ed kernel is also entered via the decompressor and needs MMIO support there, so this patch-set also adds MMIO #VC support to the decompressor and support for handling CLFLUSH instructions. Finally there is also code to disable kexec/kdump support at runtime when the environment does not support it (e.g. no GHCB protocol version 2 support or AP Jump Table over 4GB). The diffstat looks big, but most of it is moving code for MMIO #VC support around to make it available to the decompressor. Known problems: It currently only works reliable when the kexec_file syscall is used. With the kexec syscall it works one time, and the second kexec then hangs because the sha256 verification fails in the purgatory. For the kexec syscall the purgatory is loaded from user-space, were most likely the issue needs to be fixed. But the question is whether this is a useful way. The user-space purgatory has other ways to break under SEV-ES, which can be enabled via kexec-tool command line options. For example enabling console support for the purgatory will definitly break kexec for SEV-ES. So the question is whether is makes sense to only support kexec_file() under SEV-ES, where the in-kernel purgatory is used (which has less ways to break under SEV-ES). With that said, please review :) Regards, Joerg Joerg Roedel (12): kexec: Allow architecture code to opt-out at runtime x86/kexec/64: Forbid kexec when running as an SEV-ES guest x86/sev: Save and print negotiated GHCB protocol version x86/sev: Do not hardcode GHCB protocol version x86/sev: Use GHCB protocol version 2 if supported x86/sev: Cache AP Jump Table Address x86/sev: Setup code to park APs in the AP Jump Table x86/sev: Park APs on AP Jump Table with GHCB protocol version 2 x86/sev: Use AP Jump Table blob to stop CPU x86/sev: Add MMIO handling support to boot/compressed/ code x86/sev: Handle CLFLUSH MMIO events x86/sev: Support kexec under SEV-ES with AP Jump Table blob arch/x86/boot/compressed/sev.c | 56 +- arch/x86/include/asm/realmode.h | 5 + arch/x86/include/asm/sev-ap-jumptable.h | 25 + arch/x86/include/asm/sev.h | 13 +- arch/x86/kernel/machine_kexec_64.c | 12 + arch/x86/kernel/process.c | 8 + arch/x86/kernel/sev-shared.c | 333 +++++++++- arch/x86/kernel/sev.c | 494 ++++++--------- arch/x86/lib/insn-eval-shared.c | 805 ++++++++++++++++++++++++ arch/x86/lib/insn-eval.c | 802 +---------------------- arch/x86/realmode/Makefile | 9 +- arch/x86/realmode/rm/Makefile | 11 +- arch/x86/realmode/rm/header.S | 3 + arch/x86/realmode/rm/sev_ap_park.S | 89 +++ arch/x86/realmode/rmpiggy.S | 6 + arch/x86/realmode/sev/Makefile | 41 ++ arch/x86/realmode/sev/ap_jump_table.S | 130 ++++ arch/x86/realmode/sev/ap_jump_table.lds | 24 + include/linux/kexec.h | 1 + kernel/kexec.c | 14 + kernel/kexec_file.c | 9 + 21 files changed, 1764 insertions(+), 1126 deletions(-) create mode 100644 arch/x86/include/asm/sev-ap-jumptable.h create mode 100644 arch/x86/lib/insn-eval-shared.c create mode 100644 arch/x86/realmode/rm/sev_ap_park.S create mode 100644 arch/x86/realmode/sev/Makefile create mode 100644 arch/x86/realmode/sev/ap_jump_table.S create mode 100644 arch/x86/realmode/sev/ap_jump_table.lds base-commit: 2734d6c1b1a089fb593ef6a23d4b70903526fe0c -- 2.31.1
