Re: [PATCH v3 00/10] x86/sev: KEXEC/KDUMP support for SEV-ES guests

Baoquan He
2023-06-04T13:08:44Z

Hi Joerg and Tom,

On 01/27/22 at 11:10am, Joerg Roedel wrote:
> From: Joerg Roedel <jroedel@suse.de>
>
> 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.

Is there any plan for this patchset to proceed? Without this patchset,
it does fail kexec and kdump with multiple cpus.

Thanks
Baoquan

>
> 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 VMGEXIT,
> 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.
>
> The previous version of this patch-set can be found here:
>
> https://lore.kernel.org/lkml/20210913155603.28383-1-joro@8bytes.org/
>
> Please review.
>
> Thanks,
>
> Joerg
>
> Changes v2->v3:
>
> - Rebased to v5.17-rc1
> - Applied most review comments by Boris
> - Use the name 'AP jump table' consistently
> - Make kexec-disabling for unsupported guests x86-specific
> - Cleanup and consolidate patches to detect GHCB v2 protocol
> support
>
> Joerg Roedel (10):
> x86/kexec/64: Disable kexec when SEV-ES is active
> x86/sev: Save and print negotiated GHCB protocol version
> x86/sev: Set GHCB data structure version
> 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/kexec/64: Support kexec under SEV-ES with AP Jump Table Blob
>
> arch/x86/boot/compressed/sev.c | 45 +-
> arch/x86/include/asm/insn-eval.h | 1 +
> arch/x86/include/asm/realmode.h | 5 +
> arch/x86/include/asm/sev-ap-jumptable.h | 29 +
> arch/x86/include/asm/sev.h | 11 +-
> arch/x86/kernel/machine_kexec_64.c | 12 +
> arch/x86/kernel/process.c | 8 +
> arch/x86/kernel/sev-shared.c | 233 +++++-
> arch/x86/kernel/sev.c | 404 +++++------
> arch/x86/lib/insn-eval-shared.c | 913 ++++++++++++++++++++++++
> arch/x86/lib/insn-eval.c | 909 +----------------------
> arch/x86/realmode/Makefile | 9 +-
> arch/x86/realmode/rm/Makefile | 11 +-
> arch/x86/realmode/rm/header.S | 3 +
> arch/x86/realmode/rm/sev.S | 85 +++
> arch/x86/realmode/rmpiggy.S | 6 +
> arch/x86/realmode/sev/Makefile | 33 +
> arch/x86/realmode/sev/ap_jump_table.S | 131 ++++
> arch/x86/realmode/sev/ap_jump_table.lds | 24 +
> 19 files changed, 1730 insertions(+), 1142 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.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: e783362eb54cd99b2cac8b3a9aeac942e6f6ac07
> --
> 2.34.1
>