Commit c2744ed2 authored by Sean Christopherson's avatar Sean Christopherson
Browse files

KVM: Nullify async #PF worker's "apf" pointer as soon as it might be freed 



Nullify the async #PF worker's local "apf" pointer immediately after the
point where the structure can be freed by the vCPU.  The existing comment
is helpful, but easy to overlook as there is no associated code.

Update the comment to clarify that it can be freed by as soon as the lock
is dropped, as "after this point" isn't strictly accurate, nor does it
help understand what prevents the structure from being freed earlier.

Reviewed-by: default avatarXu Yilun <yilun.xu@intel.com>
Reviewed-by: default avatarVitaly Kuznetsov <vkuznets@redhat.com>
Link: https://lore.kernel.org/r/20240110011533.503302-5-seanjc@google.com


Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
parent 8284765f

virt/kvm/async_pf.c

+6 −5
Original line number Diff line number Diff line
@@ -83,13 +83,14 @@ static void async_pf_execute(struct work_struct *work) 
	apf->vcpu = NULL;

	spin_unlock(&vcpu->async_pf.lock);



	if (!IS_ENABLED(CONFIG_KVM_ASYNC_PF_SYNC) && first)

		kvm_arch_async_page_present_queued(vcpu);



	/*

	 * apf may be freed by kvm_check_async_pf_completion() after

	 * this point

	 * The apf struct may be freed by kvm_check_async_pf_completion() as

	 * soon as the lock is dropped.  Nullify it to prevent improper usage.

	 */

	apf = NULL;



	if (!IS_ENABLED(CONFIG_KVM_ASYNC_PF_SYNC) && first)

		kvm_arch_async_page_present_queued(vcpu);



	trace_kvm_async_pf_completed(addr, cr2_or_gpa);