KVM: x86: Remove obsolete disabling of page faults in kvm_arch_vcpu_put()

Remove the disabling of page faults across kvm_steal_time_set_preempted()
as KVM now accesses the steal time struct (shared with the guest) via a
cached mapping (see commit b043138246a4, "x86/KVM: Make sure
KVM_VCPU_FLUSH_TLB flag is not missed".)  The cache lookup is flagged as
atomic, thus it would be a bug if KVM tried to resolve a new pfn, i.e.
we want the splat that would be reached via might_fault().

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20210123000334.3123628-2-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c1650e26715b381f0e1470ebfab9ce4b885b5f10..18d005378a78310148c02571483a8a579d1d6233 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4040,15 +4040,6 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
        if (vcpu->preempted && !vcpu->arch.guest_state_protected)
                vcpu->arch.preempted_in_kernel = !kvm_x86_ops.get_cpl(vcpu);
 
-       /*
-        * Disable page faults because we're in atomic context here.
-        * kvm_write_guest_offset_cached() would call might_fault()
-        * that relies on pagefault_disable() to tell if there's a
-        * bug. NOTE: the write to guest memory may not go through if
-        * during postcopy live migration or if there's heavy guest
-        * paging.
-        */
-       pagefault_disable();
        /*
         * kvm_memslots() will be called by
         * kvm_write_guest_offset_cached() so take the srcu lock.
@@ -4056,7 +4047,6 @@ void kvm_arch_vcpu_put(struct kvm_vcpu *vcpu)
        idx = srcu_read_lock(&vcpu->kvm->srcu);
        kvm_steal_time_set_preempted(vcpu);
        srcu_read_unlock(&vcpu->kvm->srcu, idx);
-       pagefault_enable();
        kvm_x86_ops.vcpu_put(vcpu);
        vcpu->arch.last_host_tsc = rdtsc();
        /*