From c2744ed2230a92636f04cde48f2f7d8d3486e194 Mon Sep 17 00:00:00 2001 From: Sean Christopherson <seanjc@google.com> Date: Tue, 9 Jan 2024 17:15:33 -0800 Subject: [PATCH] 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: Xu Yilun <yilun.xu@intel.com> Reviewed-by: Vitaly Kuznetsov <vkuznets@redhat.com> Link: https://lore.kernel.org/r/20240110011533.503302-5-seanjc@google.com Signed-off-by: Sean Christopherson <seanjc@google.com> --- virt/kvm/async_pf.c | 11 ++++++----- 1 file changed, 6 insertions(+), 5 deletions(-) diff --git a/virt/kvm/async_pf.c b/virt/kvm/async_pf.c index 628f6df7609f7..99a63bad0306c 100644 --- a/virt/kvm/async_pf.c +++ b/virt/kvm/async_pf.c @@ -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); -- 2.30.2