On 22/05/2024 8:02 am, Sean Christopherson wrote:
On Wed, May 15, 2024, Kai Huang wrote:
How about we just make all emergency virtualization disable code
unconditional but not guided by CONFIG_KVM_INTEL || CONFIG_KVM_AMD, i.e.,
revert commit
261cd5ed934e ("x86/reboot: Expose VMCS crash hooks if and only if
KVM_{INTEL,AMD} is enabled")
It makes sense anyway from the perspective that it allows the out-of-tree
kernel module hypervisor to use this mechanism w/o needing to have the
kernel built with KVM enabled in Kconfig. Otherwise, strictly speaking,
IIUC, the kernel won't be able to support out-of-tree module hypervisor as
there's no other way the module can intercept emergency reboot.
Practically speaking, no one is running an out-of-tree hypervisor without either
(a) KVM being enabled in the .config, or (b) non-trivial changes to the kernel.
Just for curiosity: why b) is required to support out-of-tree hypervisor
when KVM is disabled in Kconfig? I am probably missing something.
Exposing/exporting select APIs and symbols if and only if KVM is enabled is a
a well-established pattern, and there are concrete benefits to doing so. E.g.
it allows minimizing the kernel footprint for use cases that don't want/need KVM.
This approach avoids the weirdness of the unconditional define for only
cpu_emergency_virt_cb.
I genuinely don't understand why you find it weird to unconditionally define
cpu_emergency_virt_cb. There are myriad examples throughout the kernel where a
typedef, struct, enum, etc. is declared/defined even though support for its sole
end consumer is disabled. E.g. include/linux/mm_types.h declares "struct mem_cgroup"
for pretty much the exact same reason, even though the structure is only fully
defined if CONFIG_MEMCG=y.
The only oddity here is that the API that the #ifdef that guards the usage happens
to be right below the typedef, but it shouldn't take that much brain power to
figure out why a typedef exists outside of an #ifdef.
OK. No more arguments. :-)
Thanks for this series anyway.
