[PATCH v2 0/4] Improve KVM's interaction with CPU hotplug
chao.gao at intel.com
Mon Jan 17 22:44:23 PST 2022
Changes from v1->v2: (all comments/suggestions on v1 are from Sean, thanks)
- Merged v1's patch 2 into patch 1, and v1's patch 5 into patch 6.
- Use static_call for check_processor_compatibility().
- Generate patch 2 with "git revert" and do manual changes based on that.
- Loosen the WARN_ON() in kvm_arch_check_processor_compat() instead of
- KVM always prevent incompatible CPUs from being brought up regardless of
- Use pr_warn instead of pr_info to emit logs when KVM finds offending
KVM registers its CPU hotplug callback to CPU starting section. And in the
callback, KVM enables hardware virtualization on hotplugged CPUs if any VM
is running on existing CPUs.
There are two problems in the process:
1. KVM doesn't do compatibility checks before enabling hardware
virtualization on hotplugged CPUs. This may cause #GP if VMX isn't
supported or vmentry failure if some in-use VMX features are missing on
hotplugged CPUs. Both break running VMs.
2. Callbacks in CPU STARTING section cannot fail. So, even if KVM finds
some incompatible CPUs, its callback cannot block CPU hotplug.
This series improves KVM's interaction with CPU hotplug to avoid
incompatible CPUs breaking running VMs. Following changes are made:
1. move KVM's CPU hotplug callback to ONLINE section (suggested by Thomas)
2. do compatibility checks on hotplugged CPUs.
3. abort onlining incompatible CPUs
This series is a follow-up to the discussion about KVM and CPU hotplug
Note: this series is tested only on Intel systems.
Chao Gao (4):
KVM: x86: Move check_processor_compatibility from init ops to runtime
Partially revert "KVM: Pass kvm_init()'s opaque param to additional
KVM: Rename and move CPUHP_AP_KVM_STARTING to ONLINE section
KVM: Do compatibility checks on hotplugged CPUs
arch/arm64/kvm/arm.c | 2 +-
arch/mips/kvm/mips.c | 2 +-
arch/powerpc/kvm/powerpc.c | 2 +-
arch/riscv/kvm/main.c | 2 +-
arch/s390/kvm/kvm-s390.c | 2 +-
arch/x86/include/asm/kvm-x86-ops.h | 1 +
arch/x86/include/asm/kvm_host.h | 2 +-
arch/x86/kvm/svm/svm.c | 4 +-
arch/x86/kvm/vmx/evmcs.c | 2 +-
arch/x86/kvm/vmx/evmcs.h | 2 +-
arch/x86/kvm/vmx/vmx.c | 12 +++---
arch/x86/kvm/x86.c | 16 +++++---
include/linux/cpuhotplug.h | 2 +-
include/linux/kvm_host.h | 2 +-
virt/kvm/kvm_main.c | 62 ++++++++++++++++++++----------
15 files changed, 71 insertions(+), 44 deletions(-)
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