[PATCH 5.5 159/176] KVM: x86: Remove spurious clearing of async #PF MSR

Greg Kroah-Hartman
2020-03-03T17:51:13Z

From: Sean Christopherson <sean.j.christopherson@intel.com>

commit 208050dac5ef4de5cb83ffcafa78499c94d0b5ad upstream.

Remove a bogus clearing of apf.msr_val from kvm_arch_vcpu_destroy().

apf.msr_val is only set to a non-zero value by kvm_pv_enable_async_pf(),
which is only reachable by kvm_set_msr_common(), i.e. by writing
MSR_KVM_ASYNC_PF_EN. KVM does not autonomously write said MSR, i.e.
can only be written via KVM_SET_MSRS or KVM_RUN. Since KVM_SET_MSRS and
KVM_RUN are vcpu ioctls, they require a valid vcpu file descriptor.
kvm_arch_vcpu_destroy() is only called if KVM_CREATE_VCPU fails, and KVM
declares KVM_CREATE_VCPU successful once the vcpu fd is installed and
thus visible to userspace. Ergo, apf.msr_val cannot be non-zero when
kvm_arch_vcpu_destroy() is called.

Fixes: 344d9588a9df0 ("KVM: Add PV MSR to enable asynchronous page faults delivery.")
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/x86/kvm/x86.c | 2 --
1 file changed, 2 deletions(-)

--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9227,8 +9227,6 @@ void kvm_arch_vcpu_postcreate(struct kvm

void kvm_arch_vcpu_destroy(struct kvm_vcpu *vcpu)
{
- vcpu->arch.apf.msr_val = 0;
-
kvm_arch_vcpu_free(vcpu);
}