Revert "KVM: x86: check for cr3 validity in ioctl_set_sregs"

(cherry picked from commit dc7e795e)

This reverts commit 6c20e1442bb1c62914bb85b7f4a38973d2a423ba.

To my understanding, it became obsolete with the advent of the more
robust check in mmu_alloc_roots (89da4ff17f). Moreover, it prevents
the conceptually safe pattern

 1. set sregs
 2. register mem-slots
 3. run vcpu

by setting a sticky triple fault during step 1.
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

arch/x86/kvm/x86.c

@@ -4125,13 +4125,7 @@ int kvm_arch_vcpu_ioctl_set_sregs(struct kvm_vcpu *vcpu,
 
 	vcpu->arch.cr2 = sregs->cr2;
 	mmu_reset_needed |= vcpu->arch.cr3 != sregs->cr3;
-
-	down_read(&vcpu->kvm->slots_lock);
-	if (gfn_to_memslot(vcpu->kvm, sregs->cr3 >> PAGE_SHIFT))
-		vcpu->arch.cr3 = sregs->cr3;
-	else
-		set_bit(KVM_REQ_TRIPLE_FAULT, &vcpu->requests);
-	up_read(&vcpu->kvm->slots_lock);
+	vcpu->arch.cr3 = sregs->cr3;
 
 	kvm_set_cr8(vcpu, sregs->cr8);