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

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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>
This commit is contained in:
Sean Christopherson 2024-01-09 17:15:33 -08:00
parent 8284765f03
commit c2744ed223
1 changed files with 6 additions and 5 deletions
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11
virt/kvm/async_pf.c
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@ -83,14 +83,15 @@ static void async_pf_execute(struct work_struct *work)
apf->vcpu = NULL;
spin_unlock(&vcpu->async_pf.lock);
/*
* 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);
/*
* apf may be freed by kvm_check_async_pf_completion() after
* this point
*/
trace_kvm_async_pf_completed(addr, cr2_or_gpa);
__kvm_vcpu_wake_up(vcpu);