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| author | Sean Christopherson <seanjc@google.com> | 2024-08-29 21:35:52 -0700 |
|---|---|---|
| committer | Paolo Bonzini <pbonzini@redhat.com> | 2024-09-04 11:02:33 -0400 |
| commit | 9a798b1337afe4fdcce53efa77953b068d8614f5 (patch) | |
| tree | 55b7abe12928ec95cbb8065c47644fade159524a /Documentation/virt | |
| parent | 44d17459626052a2390457e550a12cb973506b2f (diff) | |
| download | linux-9a798b1337afe4fdcce53efa77953b068d8614f5.tar.gz linux-9a798b1337afe4fdcce53efa77953b068d8614f5.tar.bz2 linux-9a798b1337afe4fdcce53efa77953b068d8614f5.zip | |
KVM: Register cpuhp and syscore callbacks when enabling hardware
Register KVM's cpuhp and syscore callback when enabling virtualization
in hardware instead of registering the callbacks during initialization,
and let the CPU up/down framework invoke the inner enable/disable
functions. Registering the callbacks during initialization makes things
more complex than they need to be, as KVM needs to be very careful about
handling races between enabling CPUs being onlined/offlined and hardware
being enabled/disabled.
Intel TDX support will require KVM to enable virtualization during KVM
initialization, i.e. will add another wrinkle to things, at which point
sorting out the potential races with kvm_usage_count would become even
more complex.
Note, using the cpuhp framework has a subtle behavioral change: enabling
will be done serially across all CPUs, whereas KVM currently sends an IPI
to all CPUs in parallel. While serializing virtualization enabling could
create undesirable latency, the issue is limited to the 0=>1 transition of
VM creation. And even that can be mitigated, e.g. by letting userspace
force virtualization to be enabled when KVM is initialized.
Cc: Chao Gao <chao.gao@intel.com>
Reviewed-by: Kai Huang <kai.huang@intel.com>
Acked-by: Kai Huang <kai.huang@intel.com>
Tested-by: Farrah Chen <farrah.chen@intel.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20240830043600.127750-3-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Diffstat (limited to 'Documentation/virt')
| -rw-r--r-- | Documentation/virt/kvm/locking.rst | 9 |
1 files changed, 5 insertions, 4 deletions
diff --git a/Documentation/virt/kvm/locking.rst b/Documentation/virt/kvm/locking.rst index c0cb5ce51c1e..be3c323888b1 100644 --- a/Documentation/virt/kvm/locking.rst +++ b/Documentation/virt/kvm/locking.rst @@ -9,7 +9,9 @@ KVM Lock Overview The acquisition orders for mutexes are as follows: -- cpus_read_lock() is taken outside kvm_lock and kvm_usage_lock +- cpus_read_lock() is taken outside kvm_lock + +- kvm_usage_lock is taken outside cpus_read_lock() - kvm->lock is taken outside vcpu->mutex @@ -241,9 +243,8 @@ time it will be set using the Dirty tracking mechanism described above. :Arch: any :Protects: - kvm_usage_count - hardware virtualization enable/disable -:Comment: Exists because using kvm_lock leads to deadlock (see earlier comment - on cpus_read_lock() vs kvm_lock). Note, KVM also disables CPU hotplug via - cpus_read_lock() when enabling/disabling virtualization. +:Comment: Exists to allow taking cpus_read_lock() while kvm_usage_count is + protected, which simplifies the virtualization enabling logic. ``kvm->mn_invalidate_lock`` ^^^^^^^^^^^^^^^^^^^^^^^^^^^ |