KVM: TDX: Guard VM state transitions with "all" the locks

Acquire kvm->lock, kvm->slots_lock, and all vcpu->mutex locks when
servicing ioctls that (a) transition the TD to a new state, i.e. when
doing INIT or FINALIZE or (b) are only valid if the TD is in a specific
state, i.e. when initializing a vCPU or memory region.  Acquiring "all"
the locks fixes several KVM_BUG_ON() situations where a SEAMCALL can fail
due to racing actions, e.g. if tdh_vp_create() contends with either
tdh_mr_extend() or tdh_mr_finalize().

For all intents and purposes, the paths in question are fully serialized,
i.e. there's no reason to try and allow anything remotely interesting to
happen.  Smack 'em with a big hammer instead of trying to be "nice".

Acquire kvm->lock to prevent VM-wide things from happening, slots_lock to
prevent kvm_mmu_zap_all_fast(), and _all_ vCPU mutexes to prevent vCPUs
from interefering.  Use the recently-renamed kvm_arch_vcpu_unlocked_ioctl()
to service the vCPU-scoped ioctls to avoid a lock inversion problem, e.g.
due to taking vcpu->mutex outside kvm->lock.

See also commit ecf371f8b02d ("KVM: SVM: Reject SEV{-ES} intra host
migration if vCPU creation is in-flight"), which fixed a similar bug with
SEV intra-host migration where an in-flight vCPU creation could race with
a VM-wide state transition.

Define a fancy new CLASS to handle the lock+check => unlock logic with
guard()-like syntax:

        CLASS(tdx_vm_state_guard, guard)(kvm);
        if (IS_ERR(guard))
                return PTR_ERR(guard);

to simplify juggling the many locks.

Note!  Take kvm->slots_lock *after* all vcpu->mutex locks, as per KVM's
soon-to-be-documented lock ordering rules[1].

Link: https://lore.kernel.org/all/20251016235538.171962-1-seanjc@google.com [1]
Reported-by: Yan Zhao <yan.y.zhao@intel.com>
Closes: https://lore.kernel.org/all/aLFiPq1smdzN3Ary@yzhao56-desk.sh.intel.com
Reviewed-by: Kai Huang <kai.huang@intel.com>
Reviewed-by: Yan Zhao <yan.y.zhao@intel.com>
Tested-by: Yan Zhao <yan.y.zhao@intel.com>
Tested-by: Kai Huang <kai.huang@intel.com>
Link: https://patch.msgid.link/20251030200951.3402865-27-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

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