Re: [PATCH v3 0/8] KVM: Register cpuhp/syscore callbacks when enabling virt

[Paolo Bonzini <pbonzini@redhat.com>]

On 6/8/24 02:06, Sean Christopherson wrote:
> Register KVM's cpuhp and syscore callbacks when enabling virtualization in
> hardware, as the sole purpose of said callbacks is to disable and re-enable
> virtualization as needed.
> 
> The primary motivation for this series is to simplify dealing with enabling
> virtualization for Intel's TDX, which needs to enable virtualization
> when kvm-intel.ko is loaded, i.e. long before the first VM is created.  TDX
> doesn't _need_ to keep virtualization enabled, but doing so is much simpler
> for KVM (see patch 3).
> 
> That said, this is a nice cleanup on its own, assuming I haven't broken
> something.  By registering the callbacks on-demand, the callbacks themselves
> don't need to check kvm_usage_count, because their very existence implies a
> non-zero count.
> 
> The meat is in patch 1.  Patches 2 renames the helpers so that patch 3 is
> less awkward.  Patch 3 adds a module param to enable virtualization when KVM
> is loaded.  Patches 4-6 are tangentially related x86 cleanups to registers
> KVM's "emergency disable" callback on-demand, same as the syscore callbacks.
> 
> The suspend/resume and cphup paths still need to be fully tested, as do
> non-x86 architectures.

Also placed in kvm/queue, mostly as a reminder to myself, and added 
other maintainers for testing on ARM, RISC-V and LoongArch.  The changes 
from v3 to v4 should be mostly nits, documentation and organization of 
the series.

Thanks,

Paolo

> v3:
>   - Collect reviews/acks.
>   - Switch to kvm_usage_lock in a dedicated patch, Cc'd for stable@. [Chao]
>   - Enable virt at load by default. [Chao]
>   - Add comments to document how kvm_arch_{en,dis}able_virtualization() fit
>     into the overall flow. [Kai]
> 
> v2:
>   - https://lore.kernel.org/all/20240522022827.1690416-1-seanjc@google.com
>   - Use a dedicated mutex to avoid lock inversion issues between kvm_lock and
>     the cpuhp lock.
>   - Register emergency disable callbacks on-demand. [Kai]
>   - Drop an unintended s/junk/ign rename. [Kai]
>   - Decrement kvm_usage_count on failure. [Chao]
> 
> v1: https://lore.kernel.org/all/20240425233951.3344485-1-seanjc@google.com
> 
> Sean Christopherson (8):
>    KVM: Use dedicated mutex to protect kvm_usage_count to avoid deadlock
>    KVM: Register cpuhp and syscore callbacks when enabling hardware
>    KVM: Rename functions related to enabling virtualization hardware
>    KVM: Add a module param to allow enabling virtualization when KVM is
>      loaded
>    KVM: Add arch hooks for enabling/disabling virtualization
>    x86/reboot: Unconditionally define cpu_emergency_virt_cb typedef
>    KVM: x86: Register "emergency disable" callbacks when virt is enabled
>    KVM: Enable virtualization at load/initialization by default
> 
>   Documentation/virt/kvm/locking.rst |  19 ++-
>   arch/x86/include/asm/kvm_host.h    |   3 +
>   arch/x86/include/asm/reboot.h      |   2 +-
>   arch/x86/kvm/svm/svm.c             |   5 +-
>   arch/x86/kvm/vmx/main.c            |   2 +
>   arch/x86/kvm/vmx/vmx.c             |   6 +-
>   arch/x86/kvm/vmx/x86_ops.h         |   1 +
>   arch/x86/kvm/x86.c                 |  10 ++
>   include/linux/kvm_host.h           |  14 ++
>   virt/kvm/kvm_main.c                | 258 ++++++++++++++---------------
>   10 files changed, 175 insertions(+), 145 deletions(-)
> 
> 
> base-commit: af0903ab52ee6d6f0f63af67fa73d5eb00f79b9a